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 $40.62   6.156%   $43.1206   $43.12   $43.10   $43.10  
  Purchase #2 $212.79   6.191%   $225.9638   $225.96   $225.95   $226.00  
  Purchase #3 $201.90   5.502%   $213.0085   $213.01   $213.00   $213.00  
  Purchase #4 $110.54   5.389%   $116.497   $116.50   $116.50   $116.50  
  Purchase #5 $31.65   5.507%   $33.393   $33.39   $33.40   $33.40  
  Purchase #6 $11.66   8.104%   $12.6049   $12.60   $12.60   $12.60  
  Purchase #7 $132.71   10.815%   $147.0626   $147.06   $147.05   $147.10  
  7 purchase totals = $741.87       $791.6504   $791.64   $791.60   $791.70