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 $57.49   12.753%   $64.8217   $64.82   $64.80   $64.80  
  Purchase #2 $215.79   10.686%   $238.8493   $238.85   $238.85   $238.80  
  Purchase #3 $97.93   7.364%   $105.1416   $105.14   $105.15   $105.10  
  Purchase #4 $240.83   3.811%   $250.008   $250.01   $250.00   $250.00  
  Purchase #5 $91.47   13.137%   $103.4864   $103.49   $103.50   $103.50  
  Purchase #6 $72.27   3.575%   $74.8537   $74.85   $74.85   $74.90  
  Purchase #7 $204.27   8.141%   $220.8996   $220.90   $220.90   $220.90  
  7 purchase totals = $980.05       $1,058.0603   $1,058.06   $1,058.05   $1,058.00