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 $250.68   6.479%   $266.9216   $266.92   $266.90   $266.90  
  Purchase #2 $178.56   12.388%   $200.68   $200.68   $200.70   $200.70  
  Purchase #3 $146.56   6.363%   $155.8856   $155.89   $155.90   $155.90  
  Purchase #4 $163.45   6.747%   $174.478   $174.48   $174.50   $174.50  
  Purchase #5 $68.80   10.286%   $75.8768   $75.88   $75.90   $75.90  
  Purchase #6 $36.26   3.818%   $37.6444   $37.64   $37.65   $37.60  
  Purchase #7 $203.75   3.580%   $211.0443   $211.04   $211.05   $211.00  
  7 purchase totals = $1,048.06       $1,122.5307   $1,122.53   $1,122.60   $1,122.50