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 $38.41   6.770%   $41.0104   $41.01   $41.00   $41.00  
  Purchase #2 $176.92   4.817%   $185.4422   $185.44   $185.45   $185.40  
  Purchase #3 $204.65   13.551%   $232.3821   $232.38   $232.40   $232.40  
  Purchase #4 $85.28   13.453%   $96.7527   $96.75   $96.75   $96.80  
  Purchase #5 $24.76   12.755%   $27.9181   $27.92   $27.90   $27.90  
  Purchase #6 $140.88   10.160%   $155.1934   $155.19   $155.20   $155.20  
  Purchase #7 $244.49   11.487%   $272.5746   $272.57   $272.55   $272.60  
  7 purchase totals = $915.39       $1,011.2735   $1,011.26   $1,011.25   $1,011.30