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 $227.30   6.696%   $242.52   $242.52   $242.50   $242.50  
  Purchase #2 $246.51   11.820%   $275.6475   $275.65   $275.65   $275.60  
  Purchase #3 $52.99   7.354%   $56.8869   $56.89   $56.90   $56.90  
  Purchase #4 $124.92   5.816%   $132.1853   $132.19   $132.20   $132.20  
  Purchase #5 $140.51   10.796%   $155.6795   $155.68   $155.70   $155.70  
  Purchase #6 $231.97   10.207%   $255.6472   $255.65   $255.65   $255.60  
  Purchase #7 $58.50   10.290%   $64.5197   $64.52   $64.50   $64.50  
  7 purchase totals = $1,082.70       $1,183.0861   $1,183.10   $1,183.10   $1,183.00