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 $48.43   6.449%   $51.5533   $51.55   $51.55   $51.60  
  Purchase #2 $214.32   11.817%   $239.6462   $239.65   $239.65   $239.60  
  Purchase #3 $80.99   11.107%   $89.9856   $89.99   $90.00   $90.00  
  Purchase #4 $222.49   9.270%   $243.1148   $243.11   $243.10   $243.10  
  Purchase #5 $240.33   7.659%   $258.7369   $258.74   $258.75   $258.70  
  Purchase #6 $10.38   10.237%   $11.4426   $11.44   $11.45   $11.40  
  Purchase #7 $157.43   10.243%   $173.5556   $173.56   $173.55   $173.60  
  7 purchase totals = $974.37       $1,068.0350   $1,068.04   $1,068.05   $1,068.00