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 $71.74   4.171%   $74.7323   $74.73   $74.75   $74.70  
  Purchase #2 $141.72   4.334%   $147.8621   $147.86   $147.85   $147.90  
  Purchase #3 $25.89   13.674%   $29.4302   $29.43   $29.45   $29.40  
  Purchase #4 $118.93   9.452%   $130.1713   $130.17   $130.15   $130.20  
  Purchase #5 $49.27   5.530%   $51.9946   $51.99   $52.00   $52.00  
  Purchase #6 $193.47   7.603%   $208.1795   $208.18   $208.20   $208.20  
  Purchase #7 $167.46   4.620%   $175.1967   $175.20   $175.20   $175.20  
  7 purchase totals = $768.48       $817.5667   $817.56   $817.60   $817.60