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 $160.80   6.763%   $171.6749   $171.67   $171.65   $171.70  
  Purchase #2 $36.86   5.808%   $39.0008   $39.00   $39.00   $39.00  
  Purchase #3 $99.45   3.272%   $102.704   $102.70   $102.70   $102.70  
  Purchase #4 $28.51   13.294%   $32.3001   $32.30   $32.30   $32.30  
  Purchase #5 $26.86   5.467%   $28.3284   $28.33   $28.35   $28.30  
  Purchase #6 $145.70   4.822%   $152.7257   $152.73   $152.75   $152.70  
  Purchase #7 $207.26   9.260%   $226.4523   $226.45   $226.45   $226.50  
  7 purchase totals = $705.44       $753.1862   $753.18   $753.20   $753.20