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 $100.76   13.689%   $114.553   $114.55   $114.55   $114.60  
  Purchase #2 $197.50   10.415%   $218.0696   $218.07   $218.05   $218.10  
  Purchase #3 $176.97   8.270%   $191.6054   $191.61   $191.60   $191.60  
  Purchase #4 $91.49   6.731%   $97.6482   $97.65   $97.65   $97.60  
  Purchase #5 $45.52   8.337%   $49.315   $49.32   $49.30   $49.30  
  Purchase #6 $78.33   13.464%   $88.8764   $88.88   $88.90   $88.90  
  Purchase #7 $122.90   5.748%   $129.9643   $129.96   $129.95   $130.00  
  7 purchase totals = $813.47       $890.0319   $890.04   $890.00   $890.10