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 $194.34   3.848%   $201.8182   $201.82   $201.80   $201.80  
  Purchase #2 $45.66   8.828%   $49.6909   $49.69   $49.70   $49.70  
  Purchase #3 $101.37   5.348%   $106.7913   $106.79   $106.80   $106.80  
  Purchase #4 $110.52   10.315%   $121.9201   $121.92   $121.90   $121.90  
  Purchase #5 $248.37   10.855%   $275.3306   $275.33   $275.35   $275.30  
  Purchase #6 $101.91   12.863%   $115.0187   $115.02   $115.00   $115.00  
  Purchase #7 $173.43   12.111%   $194.4341   $194.43   $194.45   $194.40  
  7 purchase totals = $975.60       $1,065.0039   $1,065.00   $1,065.00   $1,064.90