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 $205.82   10.663%   $227.7666   $227.77   $227.75   $227.80  
  Purchase #2 $39.75   9.488%   $43.5215   $43.52   $43.50   $43.50  
  Purchase #3 $162.43   11.223%   $180.6595   $180.66   $180.65   $180.70  
  Purchase #4 $57.26   12.297%   $64.3013   $64.30   $64.30   $64.30  
  Purchase #5 $124.68   7.383%   $133.8851   $133.89   $133.90   $133.90  
  Purchase #6 $17.87   11.814%   $19.9812   $19.98   $20.00   $20.00  
  Purchase #7 $51.37   11.563%   $57.3099   $57.31   $57.30   $57.30  
  7 purchase totals = $659.18       $727.4251   $727.43   $727.40   $727.50