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 $218.98   11.274%   $243.6678   $243.67   $243.65   $243.70  
  Purchase #2 $53.56   8.644%   $58.1897   $58.19   $58.20   $58.20  
  Purchase #3 $43.80   5.754%   $46.3203   $46.32   $46.30   $46.30  
  Purchase #4 $63.94   7.570%   $68.7803   $68.78   $68.80   $68.80  
  Purchase #5 $56.30   4.585%   $58.8814   $58.88   $58.90   $58.90  
  Purchase #6 $118.70   6.496%   $126.4108   $126.41   $126.40   $126.40  
  Purchase #7 $214.45   9.625%   $235.0908   $235.09   $235.10   $235.10  
  7 purchase totals = $769.73       $837.3411   $837.34   $837.35   $837.40