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 $246.93   3.167%   $254.7503   $254.75   $254.75   $254.80  
  Purchase #2 $78.40   9.605%   $85.9303   $85.93   $85.95   $85.90  
  Purchase #3 $95.92   8.245%   $103.8286   $103.83   $103.85   $103.80  
  Purchase #4 $14.37   7.470%   $15.4434   $15.44   $15.45   $15.40  
  Purchase #5 $71.35   5.639%   $75.3734   $75.37   $75.35   $75.40  
  Purchase #6 $239.82   8.593%   $260.4277   $260.43   $260.45   $260.40  
  Purchase #7 $205.67   3.362%   $212.5846   $212.58   $212.60   $212.60  
  7 purchase totals = $952.46       $1,008.3383   $1,008.33   $1,008.40   $1,008.30