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 $75.83   6.461%   $80.7294   $80.73   $80.75   $80.70  
  Purchase #2 $248.46   11.473%   $276.9658   $276.97   $276.95   $277.00  
  Purchase #3 $148.28   12.594%   $166.9544   $166.95   $166.95   $167.00  
  Purchase #4 $84.94   6.700%   $90.631   $90.63   $90.65   $90.60  
  Purchase #5 $64.28   6.404%   $68.3965   $68.40   $68.40   $68.40  
  Purchase #6 $72.72   6.650%   $77.5559   $77.56   $77.55   $77.60  
  Purchase #7 $191.64   5.232%   $201.6666   $201.67   $201.65   $201.70  
  7 purchase totals = $886.15       $962.8996   $962.91   $962.90   $963.00