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 $173.98   13.588%   $197.6204   $197.62   $197.60   $197.60  
  Purchase #2 $11.84   10.752%   $13.113   $13.11   $13.10   $13.10  
  Purchase #3 $216.41   10.835%   $239.858   $239.86   $239.85   $239.90  
  Purchase #4 $59.31   7.109%   $63.5263   $63.53   $63.55   $63.50  
  Purchase #5 $245.34   13.258%   $277.8672   $277.87   $277.85   $277.90  
  Purchase #6 $217.47   3.768%   $225.6643   $225.66   $225.65   $225.70  
  Purchase #7 $14.86   11.840%   $16.6194   $16.62   $16.60   $16.60  
  7 purchase totals = $939.21       $1,034.2686   $1,034.27   $1,034.20   $1,034.30