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 $103.97   13.670%   $118.1827   $118.18   $118.20   $118.20  
  Purchase #2 $228.43   5.873%   $241.8457   $241.85   $241.85   $241.80  
  Purchase #3 $156.61   12.231%   $175.765   $175.77   $175.75   $175.80  
  Purchase #4 $148.53   8.791%   $161.5873   $161.59   $161.60   $161.60  
  Purchase #5 $35.80   9.590%   $39.2332   $39.23   $39.25   $39.20  
  Purchase #6 $15.25   8.335%   $16.5211   $16.52   $16.50   $16.50  
  Purchase #7 $49.91   4.149%   $51.9808   $51.98   $52.00   $52.00  
  7 purchase totals = $738.50       $805.1158   $805.12   $805.15   $805.10