Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $166.56   3.381%   $172.1914   $172.19   $172.20   $172.20  
  Purchase #2 $206.39   10.806%   $228.6925   $228.69   $228.70   $228.70  
  Purchase #3 $246.33   9.799%   $270.4679   $270.47   $270.45   $270.50  
  Purchase #4 $228.64   12.528%   $257.284   $257.28   $257.30   $257.30  
  Purchase #5 $169.28   5.636%   $178.8206   $178.82   $178.80   $178.80  
  Purchase #6 $247.34   6.429%   $263.2415   $263.24   $263.25   $263.20  
  Purchase #7 $116.80   10.433%   $128.9857   $128.99   $129.00   $129.00  
  7 purchase totals = $1,381.34       $1,499.6836   $1,499.68   $1,499.70   $1,499.70