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 $24.64   9.379%   $26.951   $26.95   $26.95   $27.00  
  Purchase #2 $227.55   10.633%   $251.7454   $251.75   $251.75   $251.70  
  Purchase #3 $243.64   9.311%   $266.3253   $266.33   $266.35   $266.30  
  Purchase #4 $194.32   8.457%   $210.7536   $210.75   $210.75   $210.80  
  Purchase #5 $54.74   10.451%   $60.4609   $60.46   $60.45   $60.50  
  Purchase #6 $240.31   11.817%   $268.7074   $268.71   $268.70   $268.70  
  Purchase #7 $156.69   3.153%   $161.6304   $161.63   $161.65   $161.60  
  7 purchase totals = $1,141.89       $1,246.5740   $1,246.58   $1,246.60   $1,246.60