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 $214.54   13.432%   $243.357   $243.36   $243.35   $243.40  
  Purchase #2 $71.50   4.377%   $74.6296   $74.63   $74.65   $74.60  
  Purchase #3 $5.52   6.326%   $5.8692   $5.87   $5.85   $5.90  
  Purchase #4 $89.45   3.541%   $92.6174   $92.62   $92.60   $92.60  
  Purchase #5 $250.40   7.431%   $269.0072   $269.01   $269.00   $269.00  
  Purchase #6 $195.57   3.695%   $202.7963   $202.80   $202.80   $202.80  
  Purchase #7 $161.73   5.244%   $170.2111   $170.21   $170.20   $170.20  
  7 purchase totals = $988.71       $1,058.4878   $1,058.50   $1,058.45   $1,058.50