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 $44.95   4.739%   $47.0802   $47.08   $47.10   $47.10  
  Purchase #2 $187.37   10.143%   $206.3749   $206.37   $206.35   $206.40  
  Purchase #3 $107.27   10.276%   $118.2931   $118.29   $118.30   $118.30  
  Purchase #4 $184.97   10.802%   $204.9505   $204.95   $204.95   $205.00  
  Purchase #5 $131.54   3.780%   $136.5122   $136.51   $136.50   $136.50  
  Purchase #6 $118.64   8.463%   $128.6805   $128.68   $128.70   $128.70  
  Purchase #7 $125.85   13.790%   $143.2047   $143.20   $143.20   $143.20  
  7 purchase totals = $900.59       $985.0961   $985.08   $985.10   $985.20