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 $169.88   8.692%   $184.646   $184.65   $184.65   $184.60  
  Purchase #2 $73.73   13.758%   $83.8738   $83.87   $83.85   $83.90  
  Purchase #3 $126.35   3.261%   $130.4703   $130.47   $130.45   $130.50  
  Purchase #4 $51.31   8.270%   $55.5533   $55.55   $55.55   $55.60  
  Purchase #5 $198.78   12.449%   $223.5261   $223.53   $223.55   $223.50  
  Purchase #6 $22.27   8.766%   $24.2222   $24.22   $24.20   $24.20  
  Purchase #7 $115.62   8.216%   $125.1193   $125.12   $125.10   $125.10  
  7 purchase totals = $757.94       $827.4110   $827.41   $827.35   $827.40