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 $69.26   6.818%   $73.9821   $73.98   $74.00   $74.00  
  Purchase #2 $87.81   7.551%   $94.4405   $94.44   $94.45   $94.40  
  Purchase #3 $48.58   12.425%   $54.6161   $54.62   $54.60   $54.60  
  Purchase #4 $147.64   10.754%   $163.5172   $163.52   $163.50   $163.50  
  Purchase #5 $62.44   3.279%   $64.4874   $64.49   $64.50   $64.50  
  Purchase #6 $209.35   6.347%   $222.6374   $222.64   $222.65   $222.60  
  Purchase #7 $223.63   6.854%   $238.9576   $238.96   $238.95   $239.00  
  7 purchase totals = $848.71       $912.6383   $912.65   $912.65   $912.60