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 $217.35   11.402%   $242.1322   $242.13   $242.15   $242.10  
  Purchase #2 $173.89   12.554%   $195.7202   $195.72   $195.70   $195.70  
  Purchase #3 $202.33   10.421%   $223.4148   $223.41   $223.40   $223.40  
  Purchase #4 $92.96   3.279%   $96.0082   $96.01   $96.00   $96.00  
  Purchase #5 $216.35   3.699%   $224.3528   $224.35   $224.35   $224.40  
  Purchase #6 $110.92   6.398%   $118.0167   $118.02   $118.00   $118.00  
  Purchase #7 $158.27   11.478%   $176.4362   $176.44   $176.45   $176.40  
  7 purchase totals = $1,172.07       $1,276.0811   $1,276.08   $1,276.05   $1,276.00