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 $143.96   6.277%   $152.9964   $153.00   $153.00   $153.00  
  Purchase #2 $185.34   6.477%   $197.3445   $197.34   $197.35   $197.30  
  Purchase #3 $66.53   7.331%   $71.4073   $71.41   $71.40   $71.40  
  Purchase #4 $209.77   6.300%   $222.9855   $222.99   $223.00   $223.00  
  Purchase #5 $104.62   11.756%   $116.9191   $116.92   $116.90   $116.90  
  Purchase #6 $93.86   6.327%   $99.7985   $99.80   $99.80   $99.80  
  Purchase #7 $190.28   8.835%   $207.0912   $207.09   $207.10   $207.10  
  7 purchase totals = $994.36       $1,068.5425   $1,068.55   $1,068.55   $1,068.50