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 $181.59   13.863%   $206.7638   $206.76   $206.75   $206.80  
  Purchase #2 $93.28   11.478%   $103.9867   $103.99   $104.00   $104.00  
  Purchase #3 $137.44   5.763%   $145.3607   $145.36   $145.35   $145.40  
  Purchase #4 $102.93   6.802%   $109.9313   $109.93   $109.95   $109.90  
  Purchase #5 $184.96   10.298%   $204.0072   $204.01   $204.00   $204.00  
  Purchase #6 $59.88   12.353%   $67.277   $67.28   $67.30   $67.30  
  Purchase #7 $181.88   5.140%   $191.2286   $191.23   $191.25   $191.20  
  7 purchase totals = $941.96       $1,028.5553   $1,028.56   $1,028.60   $1,028.60