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 $211.49   11.182%   $235.1388   $235.14   $235.15   $235.10  
  Purchase #2 $183.48   9.106%   $200.1877   $200.19   $200.20   $200.20  
  Purchase #3 $85.25   13.383%   $96.659   $96.66   $96.65   $96.70  
  Purchase #4 $217.95   9.266%   $238.1452   $238.15   $238.15   $238.10  
  Purchase #5 $12.61   8.232%   $13.6481   $13.65   $13.65   $13.60  
  Purchase #6 $205.80   13.701%   $233.9967   $234.00   $234.00   $234.00  
  Purchase #7 $230.94   5.699%   $244.1013   $244.10   $244.10   $244.10  
  7 purchase totals = $1,147.52       $1,261.8768   $1,261.89   $1,261.90   $1,261.80