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 $235.60   13.514%   $267.439   $267.44   $267.45   $267.40  
  Purchase #2 $175.52   10.276%   $193.5564   $193.56   $193.55   $193.60  
  Purchase #3 $132.28   6.350%   $140.6798   $140.68   $140.70   $140.70  
  Purchase #4 $212.56   9.858%   $233.5142   $233.51   $233.50   $233.50  
  Purchase #5 $96.36   5.233%   $101.4025   $101.40   $101.40   $101.40  
  Purchase #6 $92.37   5.814%   $97.7404   $97.74   $97.75   $97.70  
  Purchase #7 $42.80   13.665%   $48.6486   $48.65   $48.65   $48.60  
  7 purchase totals = $987.49       $1,082.9809   $1,082.98   $1,083.00   $1,082.90