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 $58.33   10.753%   $64.6022   $64.60   $64.60   $64.60  
  Purchase #2 $244.74   5.299%   $257.7088   $257.71   $257.70   $257.70  
  Purchase #3 $31.58   10.490%   $34.8927   $34.89   $34.90   $34.90  
  Purchase #4 $23.31   10.227%   $25.6939   $25.69   $25.70   $25.70  
  Purchase #5 $125.99   9.174%   $137.5483   $137.55   $137.55   $137.50  
  Purchase #6 $119.35   5.686%   $126.1362   $126.14   $126.15   $126.10  
  Purchase #7 $131.57   7.292%   $141.1641   $141.16   $141.15   $141.20  
  7 purchase totals = $734.87       $787.7462   $787.74   $787.75   $787.70