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 $143.75   9.578%   $157.5184   $157.52   $157.50   $157.50  
  Purchase #2 $140.55   7.198%   $150.6668   $150.67   $150.65   $150.70  
  Purchase #3 $207.73   5.800%   $219.7783   $219.78   $219.80   $219.80  
  Purchase #4 $53.67   5.431%   $56.5848   $56.58   $56.60   $56.60  
  Purchase #5 $69.94   11.682%   $78.1104   $78.11   $78.10   $78.10  
  Purchase #6 $228.29   12.129%   $255.9793   $255.98   $256.00   $256.00  
  Purchase #7 $227.33   9.590%   $249.1309   $249.13   $249.15   $249.10  
  7 purchase totals = $1,071.26       $1,167.7689   $1,167.77   $1,167.80   $1,167.80