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 $235.76   11.636%   $263.193   $263.19   $263.20   $263.20  
  Purchase #2 $42.35   13.318%   $47.9902   $47.99   $48.00   $48.00  
  Purchase #3 $226.29   13.425%   $256.6694   $256.67   $256.65   $256.70  
  Purchase #4 $62.27   5.569%   $65.7378   $65.74   $65.75   $65.70  
  Purchase #5 $187.80   6.402%   $199.823   $199.82   $199.80   $199.80  
  Purchase #6 $193.33   13.668%   $219.7543   $219.75   $219.75   $219.80  
  Purchase #7 $57.82   8.755%   $62.8821   $62.88   $62.90   $62.90  
  7 purchase totals = $1,005.62       $1,116.0498   $1,116.04   $1,116.05   $1,116.10