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 $173.92   13.732%   $197.8027   $197.80   $197.80   $197.80  
  Purchase #2 $221.58   10.563%   $244.9855   $244.99   $245.00   $245.00  
  Purchase #3 $168.28   7.150%   $180.312   $180.31   $180.30   $180.30  
  Purchase #4 $184.66   8.170%   $199.7467   $199.75   $199.75   $199.70  
  Purchase #5 $127.43   13.470%   $144.5948   $144.59   $144.60   $144.60  
  Purchase #6 $40.80   7.451%   $43.84   $43.84   $43.85   $43.80  
  Purchase #7 $55.56   6.265%   $59.0408   $59.04   $59.05   $59.00  
  7 purchase totals = $972.23       $1,070.3225   $1,070.32   $1,070.35   $1,070.20