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 $207.33   9.481%   $226.987   $226.99   $227.00   $227.00  
  Purchase #2 $116.50   3.614%   $120.7103   $120.71   $120.70   $120.70  
  Purchase #3 $168.32   5.718%   $177.9445   $177.94   $177.95   $177.90  
  Purchase #4 $244.57   13.314%   $277.132   $277.13   $277.15   $277.10  
  Purchase #5 $92.38   8.162%   $99.9201   $99.92   $99.90   $99.90  
  Purchase #6 $87.82   10.830%   $97.3309   $97.33   $97.35   $97.30  
  Purchase #7 $66.30   12.220%   $74.4019   $74.40   $74.40   $74.40  
  7 purchase totals = $983.22       $1,074.4267   $1,074.42   $1,074.45   $1,074.30