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 $90.45   5.811%   $95.706   $95.71   $95.70   $95.70  
  Purchase #2 $212.73   7.783%   $229.2868   $229.29   $229.30   $229.30  
  Purchase #3 $123.28   5.364%   $129.8927   $129.89   $129.90   $129.90  
  Purchase #4 $243.32   10.505%   $268.8808   $268.88   $268.90   $268.90  
  Purchase #5 $149.32   7.688%   $160.7997   $160.80   $160.80   $160.80  
  Purchase #6 $211.70   9.233%   $231.2463   $231.25   $231.25   $231.20  
  Purchase #7 $233.67   13.626%   $265.5099   $265.51   $265.50   $265.50  
  7 purchase totals = $1,264.47       $1,381.3222   $1,381.33   $1,381.35   $1,381.30