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 $76.72   9.284%   $83.8427   $83.84   $83.85   $83.80  
  Purchase #2 $234.94   8.620%   $255.1918   $255.19   $255.20   $255.20  
  Purchase #3 $183.43   10.444%   $202.5874   $202.59   $202.60   $202.60  
  Purchase #4 $9.68   4.684%   $10.1334   $10.13   $10.15   $10.10  
  Purchase #5 $247.84   13.781%   $281.9948   $281.99   $282.00   $282.00  
  Purchase #6 $69.58   7.747%   $74.9704   $74.97   $74.95   $75.00  
  Purchase #7 $95.33   10.654%   $105.4865   $105.49   $105.50   $105.50  
  7 purchase totals = $917.52       $1,014.2070   $1,014.20   $1,014.25   $1,014.20