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 $167.83   9.667%   $184.0541   $184.05   $184.05   $184.10  
  Purchase #2 $25.47   7.480%   $27.3752   $27.38   $27.40   $27.40  
  Purchase #3 $66.45   4.765%   $69.6163   $69.62   $69.60   $69.60  
  Purchase #4 $205.54   7.496%   $220.9473   $220.95   $220.95   $220.90  
  Purchase #5 $181.41   8.842%   $197.4503   $197.45   $197.45   $197.50  
  Purchase #6 $213.67   7.235%   $229.129   $229.13   $229.15   $229.10  
  Purchase #7 $111.49   12.294%   $125.1966   $125.20   $125.20   $125.20  
  7 purchase totals = $971.86       $1,053.7688   $1,053.78   $1,053.80   $1,053.80