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 $48.80   7.803%   $52.6079   $52.61   $52.60   $52.60  
  Purchase #2 $232.30   7.792%   $250.4008   $250.40   $250.40   $250.40  
  Purchase #3 $30.59   8.751%   $33.2669   $33.27   $33.25   $33.30  
  Purchase #4 $188.38   13.193%   $213.233   $213.23   $213.25   $213.20  
  Purchase #5 $243.49   13.850%   $277.2134   $277.21   $277.20   $277.20  
  Purchase #6 $120.74   13.110%   $136.569   $136.57   $136.55   $136.60  
  Purchase #7 $82.85   12.870%   $93.5128   $93.51   $93.50   $93.50  
  7 purchase totals = $947.15       $1,056.8038   $1,056.80   $1,056.75   $1,056.80