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 $59.68   5.431%   $62.9212   $62.92   $62.90   $62.90  
  Purchase #2 $45.52   8.426%   $49.3555   $49.36   $49.35   $49.40  
  Purchase #3 $171.26   11.874%   $191.5954   $191.60   $191.60   $191.60  
  Purchase #4 $219.83   10.870%   $243.7255   $243.73   $243.75   $243.70  
  Purchase #5 $106.70   12.315%   $119.8401   $119.84   $119.85   $119.80  
  Purchase #6 $174.70   5.623%   $184.5234   $184.52   $184.50   $184.50  
  Purchase #7 $62.59   3.386%   $64.7093   $64.71   $64.70   $64.70  
  7 purchase totals = $840.28       $916.6704   $916.68   $916.65   $916.60