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 $180.92   12.761%   $204.0072   $204.01   $204.00   $204.00  
  Purchase #2 $62.51   8.215%   $67.6452   $67.65   $67.65   $67.60  
  Purchase #3 $229.98   6.864%   $245.7658   $245.77   $245.75   $245.80  
  Purchase #4 $248.75   6.816%   $265.7048   $265.70   $265.70   $265.70  
  Purchase #5 $249.48   10.148%   $274.7972   $274.80   $274.80   $274.80  
  Purchase #6 $62.86   3.391%   $64.9916   $64.99   $65.00   $65.00  
  Purchase #7 $33.84   10.320%   $37.3323   $37.33   $37.35   $37.30  
  7 purchase totals = $1,068.34       $1,160.2441   $1,160.25   $1,160.25   $1,160.20