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 $49.71   4.692%   $52.0424   $52.04   $52.05   $52.00  
  Purchase #2 $200.25   7.646%   $215.5611   $215.56   $215.55   $215.60  
  Purchase #3 $111.70   3.279%   $115.3626   $115.36   $115.35   $115.40  
  Purchase #4 $202.94   4.262%   $211.5893   $211.59   $211.60   $211.60  
  Purchase #5 $16.97   9.365%   $18.5592   $18.56   $18.55   $18.60  
  Purchase #6 $23.84   12.310%   $26.7747   $26.77   $26.75   $26.80  
  Purchase #7 $160.25   9.700%   $175.7943   $175.79   $175.80   $175.80  
  7 purchase totals = $765.66       $815.6836   $815.67   $815.65   $815.80