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 $56.52   4.764%   $59.2126   $59.21   $59.20   $59.20  
  Purchase #2 $186.26   4.539%   $194.7143   $194.71   $194.70   $194.70  
  Purchase #3 $45.73   8.530%   $49.6308   $49.63   $49.65   $49.60  
  Purchase #4 $147.73   7.187%   $158.3474   $158.35   $158.35   $158.30  
  Purchase #5 $206.40   9.254%   $225.5003   $225.50   $225.50   $225.50  
  Purchase #6 $201.45   6.254%   $214.0487   $214.05   $214.05   $214.00  
  Purchase #7 $75.95   12.120%   $85.1551   $85.16   $85.15   $85.20  
  7 purchase totals = $920.04       $986.6092   $986.61   $986.60   $986.50