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 $227.62   11.347%   $253.448   $253.45   $253.45   $253.40  
  Purchase #2 $144.51   13.114%   $163.461   $163.46   $163.45   $163.50  
  Purchase #3 $68.56   12.225%   $76.9415   $76.94   $76.95   $76.90  
  Purchase #4 $234.79   5.334%   $247.3137   $247.31   $247.30   $247.30  
  Purchase #5 $27.42   12.478%   $30.8415   $30.84   $30.85   $30.80  
  Purchase #6 $204.33   3.284%   $211.0402   $211.04   $211.05   $211.00  
  Purchase #7 $48.52   10.446%   $53.5884   $53.59   $53.60   $53.60  
  7 purchase totals = $955.75       $1,036.6343   $1,036.63   $1,036.65   $1,036.50