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 $198.29   13.458%   $224.9759   $224.98   $225.00   $225.00  
  Purchase #2 $91.53   12.138%   $102.6399   $102.64   $102.65   $102.60  
  Purchase #3 $62.93   3.701%   $65.259   $65.26   $65.25   $65.30  
  Purchase #4 $171.31   11.752%   $191.4424   $191.44   $191.45   $191.40  
  Purchase #5 $199.88   3.251%   $206.3781   $206.38   $206.40   $206.40  
  Purchase #6 $107.83   11.593%   $120.3307   $120.33   $120.35   $120.30  
  Purchase #7 $127.68   11.645%   $142.5483   $142.55   $142.55   $142.50  
  7 purchase totals = $959.45       $1,053.5743   $1,053.58   $1,053.65   $1,053.50