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 $194.68   4.654%   $203.7404   $203.74   $203.75   $203.70  
  Purchase #2 $62.41   7.230%   $66.9222   $66.92   $66.90   $66.90  
  Purchase #3 $193.41   3.346%   $199.8815   $199.88   $199.90   $199.90  
  Purchase #4 $214.68   3.161%   $221.466   $221.47   $221.45   $221.50  
  Purchase #5 $172.70   9.632%   $189.3345   $189.33   $189.35   $189.30  
  Purchase #6 $83.57   8.709%   $90.8481   $90.85   $90.85   $90.80  
  Purchase #7 $88.54   11.490%   $98.7132   $98.71   $98.70   $98.70  
  7 purchase totals = $1,009.99       $1,070.9059   $1,070.90   $1,070.90   $1,070.80