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 $153.89   10.387%   $169.8746   $169.87   $169.85   $169.90  
  Purchase #2 $172.39   3.582%   $178.565   $178.57   $178.55   $178.60  
  Purchase #3 $111.73   6.646%   $119.1556   $119.16   $119.15   $119.20  
  Purchase #4 $131.73   9.163%   $143.8004   $143.80   $143.80   $143.80  
  Purchase #5 $229.27   9.721%   $251.5573   $251.56   $251.55   $251.60  
  Purchase #6 $75.56   13.151%   $85.4969   $85.50   $85.50   $85.50  
  Purchase #7 $245.35   3.685%   $254.3911   $254.39   $254.40   $254.40  
  7 purchase totals = $1,119.92       $1,202.8409   $1,202.85   $1,202.80   $1,203.00