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 $229.32   6.546%   $244.3313   $244.33   $244.35   $244.30  
  Purchase #2 $194.47   8.628%   $211.2489   $211.25   $211.25   $211.20  
  Purchase #3 $54.94   9.650%   $60.2417   $60.24   $60.25   $60.20  
  Purchase #4 $210.30   9.631%   $230.554   $230.55   $230.55   $230.60  
  Purchase #5 $52.44   6.104%   $55.6409   $55.64   $55.65   $55.60  
  Purchase #6 $181.68   6.410%   $193.3257   $193.33   $193.35   $193.30  
  Purchase #7 $24.68   11.197%   $27.4434   $27.44   $27.45   $27.40  
  7 purchase totals = $947.83       $1,022.7859   $1,022.78   $1,022.85   $1,022.60