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 $133.31   11.461%   $148.5887   $148.59   $148.60   $148.60  
  Purchase #2 $171.63   12.377%   $192.8726   $192.87   $192.85   $192.90  
  Purchase #3 $59.91   4.743%   $62.7515   $62.75   $62.75   $62.80  
  Purchase #4 $194.70   12.529%   $219.094   $219.09   $219.10   $219.10  
  Purchase #5 $21.69   13.438%   $24.6047   $24.60   $24.60   $24.60  
  Purchase #6 $169.89   6.451%   $180.8496   $180.85   $180.85   $180.80  
  Purchase #7 $180.73   6.527%   $192.5262   $192.53   $192.55   $192.50  
  7 purchase totals = $931.86       $1,021.2873   $1,021.28   $1,021.30   $1,021.30