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 $76.66   8.354%   $83.0642   $83.06   $83.05   $83.10  
  Purchase #2 $207.66   6.805%   $221.7913   $221.79   $221.80   $221.80  
  Purchase #3 $164.32   10.143%   $180.987   $180.99   $181.00   $181.00  
  Purchase #4 $91.58   7.519%   $98.4659   $98.47   $98.45   $98.50  
  Purchase #5 $230.49   7.432%   $247.62   $247.62   $247.60   $247.60  
  Purchase #6 $169.47   6.826%   $181.038   $181.04   $181.05   $181.00  
  Purchase #7 $54.85   7.547%   $58.9895   $58.99   $59.00   $59.00  
  7 purchase totals = $995.03       $1,071.9559   $1,071.96   $1,071.95   $1,072.00