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 $39.78   9.657%   $43.6216   $43.62   $43.60   $43.60  
  Purchase #2 $76.44   12.410%   $85.9262   $85.93   $85.95   $85.90  
  Purchase #3 $211.57   8.722%   $230.0231   $230.02   $230.00   $230.00  
  Purchase #4 $200.83   8.377%   $217.6535   $217.65   $217.65   $217.70  
  Purchase #5 $48.76   9.516%   $53.4   $53.40   $53.40   $53.40  
  Purchase #6 $132.98   10.259%   $146.6224   $146.62   $146.60   $146.60  
  Purchase #7 $147.27   9.214%   $160.8395   $160.84   $160.85   $160.80  
  7 purchase totals = $857.63       $938.0863   $938.08   $938.05   $938.00