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 $56.59   5.715%   $59.8241   $59.82   $59.80   $59.80  
  Purchase #2 $224.57   5.856%   $237.7208   $237.72   $237.70   $237.70  
  Purchase #3 $102.90   6.124%   $109.2016   $109.20   $109.20   $109.20  
  Purchase #4 $172.45   3.341%   $178.2116   $178.21   $178.20   $178.20  
  Purchase #5 $39.70   8.321%   $43.0034   $43.00   $43.00   $43.00  
  Purchase #6 $112.52   9.180%   $122.8493   $122.85   $122.85   $122.80  
  Purchase #7 $69.80   7.673%   $75.1558   $75.16   $75.15   $75.20  
  7 purchase totals = $778.53       $825.9666   $825.96   $825.90   $825.90