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 $108.37   3.717%   $112.3981   $112.40   $112.40   $112.40  
  Purchase #2 $125.52   3.247%   $129.5956   $129.60   $129.60   $129.60  
  Purchase #3 $11.85   12.676%   $13.3521   $13.35   $13.35   $13.40  
  Purchase #4 $128.50   10.640%   $142.1724   $142.17   $142.15   $142.20  
  Purchase #5 $36.29   9.318%   $39.6715   $39.67   $39.65   $39.70  
  Purchase #6 $109.68   7.593%   $118.008   $118.01   $118.00   $118.00  
  Purchase #7 $234.92   6.635%   $250.5069   $250.51   $250.50   $250.50  
  7 purchase totals = $755.13       $805.7046   $805.71   $805.65   $805.80