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 $48.93   12.143%   $54.8716   $54.87   $54.85   $54.90  
  Purchase #2 $76.64   10.818%   $84.9309   $84.93   $84.95   $84.90  
  Purchase #3 $96.79   13.178%   $109.545   $109.55   $109.55   $109.50  
  Purchase #4 $207.56   13.102%   $234.7545   $234.75   $234.75   $234.80  
  Purchase #5 $221.86   4.600%   $232.0656   $232.07   $232.05   $232.10  
  Purchase #6 $178.98   8.172%   $193.6062   $193.61   $193.60   $193.60  
  Purchase #7 $140.30   4.434%   $146.5209   $146.52   $146.50   $146.50  
  7 purchase totals = $971.06       $1,056.2947   $1,056.30   $1,056.25   $1,056.30