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 $48.51   8.793%   $52.7755   $52.78   $52.80   $52.80  
  Purchase #2 $116.75   13.315%   $132.2953   $132.30   $132.30   $132.30  
  Purchase #3 $71.79   5.644%   $75.8418   $75.84   $75.85   $75.80  
  Purchase #4 $68.70   9.356%   $75.1276   $75.13   $75.15   $75.10  
  Purchase #5 $165.87   12.497%   $186.5988   $186.60   $186.60   $186.60  
  Purchase #6 $148.80   11.499%   $165.9105   $165.91   $165.90   $165.90  
  Purchase #7 $196.86   4.648%   $206.0101   $206.01   $206.00   $206.00  
  7 purchase totals = $817.28       $894.5596   $894.57   $894.60   $894.50