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 $225.73   8.623%   $245.1947   $245.19   $245.20   $245.20  
  Purchase #2 $193.66   9.360%   $211.7866   $211.79   $211.80   $211.80  
  Purchase #3 $60.28   8.255%   $65.2561   $65.26   $65.25   $65.30  
  Purchase #4 $218.92   4.535%   $228.848   $228.85   $228.85   $228.80  
  Purchase #5 $219.91   12.329%   $247.0227   $247.02   $247.00   $247.00  
  Purchase #6 $214.74   9.829%   $235.8468   $235.85   $235.85   $235.80  
  Purchase #7 $63.52   6.148%   $67.4252   $67.43   $67.45   $67.40  
  7 purchase totals = $1,196.76       $1,301.3801   $1,301.39   $1,301.40   $1,301.30