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 $236.35   4.404%   $246.7589   $246.76   $246.75   $246.80  
  Purchase #2 $24.83   4.418%   $25.927   $25.93   $25.95   $25.90  
  Purchase #3 $177.35   9.336%   $193.9074   $193.91   $193.90   $193.90  
  Purchase #4 $213.89   11.480%   $238.4446   $238.44   $238.45   $238.40  
  Purchase #5 $180.49   12.163%   $202.443   $202.44   $202.45   $202.40  
  Purchase #6 $167.70   3.819%   $174.1045   $174.10   $174.10   $174.10  
  Purchase #7 $150.97   10.631%   $167.0196   $167.02   $167.00   $167.00  
  7 purchase totals = $1,151.58       $1,248.6050   $1,248.60   $1,248.60   $1,248.50