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 $241.43   11.121%   $268.2794   $268.28   $268.30   $268.30  
  Purchase #2 $223.47   12.197%   $250.7266   $250.73   $250.75   $250.70  
  Purchase #3 $170.69   12.821%   $192.5742   $192.57   $192.55   $192.60  
  Purchase #4 $68.63   7.544%   $73.8074   $73.81   $73.80   $73.80  
  Purchase #5 $79.27   10.478%   $87.5759   $87.58   $87.60   $87.60  
  Purchase #6 $108.69   9.305%   $118.8036   $118.80   $118.80   $118.80  
  Purchase #7 $207.84   7.869%   $224.1949   $224.19   $224.20   $224.20  
  7 purchase totals = $1,100.02       $1,215.9620   $1,215.96   $1,216.00   $1,216.00