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 $204.92   10.568%   $226.5759   $226.58   $226.60   $226.60  
  Purchase #2 $236.67   6.235%   $251.4264   $251.43   $251.45   $251.40  
  Purchase #3 $25.69   3.872%   $26.6847   $26.68   $26.70   $26.70  
  Purchase #4 $51.68   4.571%   $54.0423   $54.04   $54.05   $54.00  
  Purchase #5 $11.27   13.307%   $12.7697   $12.77   $12.75   $12.80  
  Purchase #6 $34.34   9.273%   $37.5243   $37.52   $37.50   $37.50  
  Purchase #7 $230.81   12.487%   $259.6312   $259.63   $259.65   $259.60  
  7 purchase totals = $795.38       $868.6545   $868.65   $868.70   $868.60