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 $50.70   3.206%   $52.3254   $52.33   $52.35   $52.30  
  Purchase #2 $240.48   10.418%   $265.5332   $265.53   $265.55   $265.50  
  Purchase #3 $234.86   3.516%   $243.1177   $243.12   $243.10   $243.10  
  Purchase #4 $116.76   4.235%   $121.7048   $121.70   $121.70   $121.70  
  Purchase #5 $228.29   10.237%   $251.66   $251.66   $251.65   $251.70  
  Purchase #6 $31.79   3.330%   $32.8486   $32.85   $32.85   $32.80  
  Purchase #7 $228.43   5.277%   $240.4843   $240.48   $240.50   $240.50  
  7 purchase totals = $1,131.31       $1,207.6740   $1,207.67   $1,207.70   $1,207.60