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 $53.52   9.445%   $58.575   $58.58   $58.60   $58.60  
  Purchase #2 $21.42   10.450%   $23.6584   $23.66   $23.65   $23.70  
  Purchase #3 $87.34   9.184%   $95.3613   $95.36   $95.35   $95.40  
  Purchase #4 $193.34   5.362%   $203.7069   $203.71   $203.70   $203.70  
  Purchase #5 $217.28   13.736%   $247.1256   $247.13   $247.15   $247.10  
  Purchase #6 $201.44   9.816%   $221.2134   $221.21   $221.20   $221.20  
  Purchase #7 $58.95   7.791%   $63.5428   $63.54   $63.55   $63.50  
  7 purchase totals = $833.29       $913.1834   $913.19   $913.20   $913.20