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 $118.39   12.822%   $133.57   $133.57   $133.55   $133.60  
  Purchase #2 $242.37   6.854%   $258.982   $258.98   $259.00   $259.00  
  Purchase #3 $106.86   12.867%   $120.6097   $120.61   $120.60   $120.60  
  Purchase #4 $172.81   6.653%   $184.307   $184.31   $184.30   $184.30  
  Purchase #5 $102.28   7.232%   $109.6769   $109.68   $109.70   $109.70  
  Purchase #6 $65.60   5.472%   $69.1896   $69.19   $69.20   $69.20  
  Purchase #7 $212.57   8.334%   $230.2856   $230.29   $230.30   $230.30  
  7 purchase totals = $1,020.88       $1,106.6208   $1,106.63   $1,106.65   $1,106.70