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 $71.70   5.476%   $75.6263   $75.63   $75.65   $75.60  
  Purchase #2 $134.37   9.646%   $147.3313   $147.33   $147.35   $147.30  
  Purchase #3 $138.58   3.598%   $143.5661   $143.57   $143.55   $143.60  
  Purchase #4 $219.33   9.587%   $240.3572   $240.36   $240.35   $240.40  
  Purchase #5 $25.44   6.297%   $27.042   $27.04   $27.05   $27.00  
  Purchase #6 $189.98   5.163%   $199.7887   $199.79   $199.80   $199.80  
  Purchase #7 $125.67   6.395%   $133.7066   $133.71   $133.70   $133.70  
  7 purchase totals = $905.07       $967.4182   $967.43   $967.45   $967.40