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 $181.86   5.212%   $191.3385   $191.34   $191.35   $191.30  
  Purchase #2 $84.95   11.635%   $94.8339   $94.83   $94.85   $94.80  
  Purchase #3 $129.36   5.855%   $136.934   $136.93   $136.95   $136.90  
  Purchase #4 $246.84   3.696%   $255.9632   $255.96   $255.95   $256.00  
  Purchase #5 $45.90   10.431%   $50.6878   $50.69   $50.70   $50.70  
  Purchase #6 $228.47   3.610%   $236.7178   $236.72   $236.70   $236.70  
  Purchase #7 $238.37   3.352%   $246.3602   $246.36   $246.35   $246.40  
  7 purchase totals = $1,155.75       $1,212.8354   $1,212.83   $1,212.85   $1,212.80