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 $231.85   13.566%   $263.3028   $263.30   $263.30   $263.30  
  Purchase #2 $121.30   11.651%   $135.4327   $135.43   $135.45   $135.40  
  Purchase #3 $32.95   3.352%   $34.0545   $34.05   $34.05   $34.10  
  Purchase #4 $188.46   11.850%   $210.7925   $210.79   $210.80   $210.80  
  Purchase #5 $198.67   13.578%   $225.6454   $225.65   $225.65   $225.60  
  Purchase #6 $58.86   11.266%   $65.4912   $65.49   $65.50   $65.50  
  Purchase #7 $115.33   9.504%   $126.291   $126.29   $126.30   $126.30  
  7 purchase totals = $947.42       $1,061.0101   $1,061.00   $1,061.05   $1,061.00