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 $47.46   10.285%   $52.3413   $52.34   $52.35   $52.30  
  Purchase #2 $64.69   4.278%   $67.4574   $67.46   $67.45   $67.50  
  Purchase #3 $26.62   9.666%   $29.1931   $29.19   $29.20   $29.20  
  Purchase #4 $59.73   6.740%   $63.7558   $63.76   $63.75   $63.80  
  Purchase #5 $226.96   13.855%   $258.4053   $258.41   $258.40   $258.40  
  Purchase #6 $139.94   10.827%   $155.0913   $155.09   $155.10   $155.10  
  Purchase #7 $235.55   6.398%   $250.6205   $250.62   $250.60   $250.60  
  7 purchase totals = $800.95       $876.8647   $876.87   $876.85   $876.90