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 $87.35   10.520%   $96.5392   $96.54   $96.55   $96.50  
  Purchase #2 $125.67   4.683%   $131.5551   $131.56   $131.55   $131.60  
  Purchase #3 $182.97   10.708%   $202.5624   $202.56   $202.55   $202.60  
  Purchase #4 $226.59   10.560%   $250.5179   $250.52   $250.50   $250.50  
  Purchase #5 $103.67   9.236%   $113.245   $113.25   $113.25   $113.20  
  Purchase #6 $148.78   4.370%   $155.2817   $155.28   $155.30   $155.30  
  Purchase #7 $84.49   9.111%   $92.1879   $92.19   $92.20   $92.20  
  7 purchase totals = $959.52       $1,041.8892   $1,041.90   $1,041.90   $1,041.90