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 $145.67   10.589%   $161.095   $161.10   $161.10   $161.10  
  Purchase #2 $152.29   9.262%   $166.3951   $166.40   $166.40   $166.40  
  Purchase #3 $20.31   9.196%   $22.1777   $22.18   $22.20   $22.20  
  Purchase #4 $8.26   7.752%   $8.9003   $8.90   $8.90   $8.90  
  Purchase #5 $19.87   13.630%   $22.5783   $22.58   $22.60   $22.60  
  Purchase #6 $80.52   11.479%   $89.7629   $89.76   $89.75   $89.80  
  Purchase #7 $49.91   3.864%   $51.8385   $51.84   $51.85   $51.80  
  7 purchase totals = $476.83       $522.7478   $522.76   $522.80   $522.80