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 $226.64   7.550%   $243.7513   $243.75   $243.75   $243.80  
  Purchase #2 $136.38   8.228%   $147.6013   $147.60   $147.60   $147.60  
  Purchase #3 $135.98   5.543%   $143.5174   $143.52   $143.50   $143.50  
  Purchase #4 $25.31   12.513%   $28.477   $28.48   $28.50   $28.50  
  Purchase #5 $180.64   11.449%   $201.3215   $201.32   $201.30   $201.30  
  Purchase #6 $111.77   6.520%   $119.0574   $119.06   $119.05   $119.10  
  Purchase #7 $69.34   9.690%   $76.059   $76.06   $76.05   $76.10  
  7 purchase totals = $886.06       $959.7849   $959.79   $959.75   $959.90