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 $216.33   7.246%   $232.0053   $232.01   $232.00   $232.00  
  Purchase #2 $48.57   13.280%   $55.0201   $55.02   $55.00   $55.00  
  Purchase #3 $117.85   11.378%   $131.259   $131.26   $131.25   $131.30  
  Purchase #4 $145.75   5.481%   $153.7386   $153.74   $153.75   $153.70  
  Purchase #5 $91.79   12.212%   $102.9994   $103.00   $103.00   $103.00  
  Purchase #6 $113.27   7.582%   $121.8581   $121.86   $121.85   $121.90  
  Purchase #7 $94.50   5.180%   $99.3951   $99.40   $99.40   $99.40  
  7 purchase totals = $828.06       $896.2756   $896.29   $896.25   $896.30