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 $110.60   5.771%   $116.9827   $116.98   $117.00   $117.00  
  Purchase #2 $10.96   11.626%   $12.2342   $12.23   $12.25   $12.20  
  Purchase #3 $34.64   11.563%   $38.6454   $38.65   $38.65   $38.60  
  Purchase #4 $49.68   10.584%   $54.9381   $54.94   $54.95   $54.90  
  Purchase #5 $180.82   12.372%   $203.1911   $203.19   $203.20   $203.20  
  Purchase #6 $110.45   10.254%   $121.7755   $121.78   $121.80   $121.80  
  Purchase #7 $247.66   5.238%   $260.6324   $260.63   $260.65   $260.60  
  7 purchase totals = $744.81       $808.3994   $808.40   $808.50   $808.30