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 $53.50   11.252%   $59.5198   $59.52   $59.50   $59.50  
  Purchase #2 $186.79   8.810%   $203.2462   $203.25   $203.25   $203.20  
  Purchase #3 $171.60   9.246%   $187.4661   $187.47   $187.45   $187.50  
  Purchase #4 $180.91   6.554%   $192.7668   $192.77   $192.75   $192.80  
  Purchase #5 $62.34   5.802%   $65.957   $65.96   $65.95   $66.00  
  Purchase #6 $87.40   5.496%   $92.2035   $92.20   $92.20   $92.20  
  Purchase #7 $184.37   4.416%   $192.5118   $192.51   $192.50   $192.50  
  7 purchase totals = $926.91       $993.6712   $993.68   $993.60   $993.70