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 $65.59   11.531%   $73.1532   $73.15   $73.15   $73.20  
  Purchase #2 $229.25   8.341%   $248.3717   $248.37   $248.35   $248.40  
  Purchase #3 $249.73   5.540%   $263.565   $263.57   $263.55   $263.60  
  Purchase #4 $31.77   5.621%   $33.5558   $33.56   $33.55   $33.60  
  Purchase #5 $195.29   3.578%   $202.2775   $202.28   $202.30   $202.30  
  Purchase #6 $110.54   7.652%   $118.9985   $119.00   $119.00   $119.00  
  Purchase #7 $173.72   9.661%   $190.5031   $190.50   $190.50   $190.50  
  7 purchase totals = $1,055.89       $1,130.4248   $1,130.43   $1,130.40   $1,130.60