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 $149.25   5.866%   $158.005   $158.01   $158.00   $158.00  
  Purchase #2 $250.81   6.189%   $266.3326   $266.33   $266.35   $266.30  
  Purchase #3 $247.59   5.317%   $260.7544   $260.75   $260.75   $260.80  
  Purchase #4 $201.74   12.608%   $227.1754   $227.18   $227.20   $227.20  
  Purchase #5 $156.96   4.637%   $164.2382   $164.24   $164.25   $164.20  
  Purchase #6 $238.37   13.622%   $270.8408   $270.84   $270.85   $270.80  
  Purchase #7 $85.54   3.185%   $88.2644   $88.26   $88.25   $88.30  
  7 purchase totals = $1,330.26       $1,435.6108   $1,435.61   $1,435.65   $1,435.60