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 $171.44   8.662%   $186.2901   $186.29   $186.30   $186.30  
  Purchase #2 $133.43   4.322%   $139.1968   $139.20   $139.20   $139.20  
  Purchase #3 $184.61   9.602%   $202.3363   $202.34   $202.35   $202.30  
  Purchase #4 $48.85   10.419%   $53.9397   $53.94   $53.95   $53.90  
  Purchase #5 $194.41   8.538%   $211.0087   $211.01   $211.00   $211.00  
  Purchase #6 $37.29   11.697%   $41.6518   $41.65   $41.65   $41.70  
  Purchase #7 $178.57   5.874%   $189.0592   $189.06   $189.05   $189.10  
  7 purchase totals = $948.60       $1,023.4826   $1,023.49   $1,023.50   $1,023.50