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 $182.53   3.715%   $189.311   $189.31   $189.30   $189.30  
  Purchase #2 $232.51   12.179%   $260.8274   $260.83   $260.85   $260.80  
  Purchase #3 $75.28   12.181%   $84.4499   $84.45   $84.45   $84.40  
  Purchase #4 $23.26   9.351%   $25.435   $25.44   $25.45   $25.40  
  Purchase #5 $211.67   6.309%   $225.0243   $225.02   $225.00   $225.00  
  Purchase #6 $219.36   11.756%   $245.148   $245.15   $245.15   $245.10  
  Purchase #7 $177.91   10.203%   $196.0622   $196.06   $196.05   $196.10  
  7 purchase totals = $1,122.52       $1,226.2578   $1,226.26   $1,226.25   $1,226.10