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 $61.35   11.346%   $68.3108   $68.31   $68.30   $68.30  
  Purchase #2 $64.26   10.657%   $71.1082   $71.11   $71.10   $71.10  
  Purchase #3 $153.95   11.199%   $171.1909   $171.19   $171.20   $171.20  
  Purchase #4 $176.95   13.717%   $201.2222   $201.22   $201.20   $201.20  
  Purchase #5 $234.45   3.822%   $243.4107   $243.41   $243.40   $243.40  
  Purchase #6 $59.83   8.724%   $65.0496   $65.05   $65.05   $65.00  
  Purchase #7 $162.62   3.449%   $168.2288   $168.23   $168.25   $168.20  
  7 purchase totals = $913.41       $988.5212   $988.52   $988.50   $988.40