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 $246.97   11.326%   $274.9418   $274.94   $274.95   $274.90  
  Purchase #2 $59.39   12.664%   $66.9111   $66.91   $66.90   $66.90  
  Purchase #3 $149.80   6.867%   $160.0868   $160.09   $160.10   $160.10  
  Purchase #4 $234.61   12.104%   $263.0072   $263.01   $263.00   $263.00  
  Purchase #5 $205.94   12.484%   $231.6495   $231.65   $231.65   $231.60  
  Purchase #6 $6.82   4.482%   $7.1257   $7.13   $7.15   $7.10  
  Purchase #7 $149.76   10.184%   $165.0116   $165.01   $165.00   $165.00  
  7 purchase totals = $1,053.29       $1,168.7337   $1,168.74   $1,168.75   $1,168.60