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 $82.37   12.871%   $92.9718   $92.97   $92.95   $93.00  
  Purchase #2 $232.43   11.310%   $258.7178   $258.72   $258.70   $258.70  
  Purchase #3 $16.43   3.293%   $16.971   $16.97   $16.95   $17.00  
  Purchase #4 $210.45   7.365%   $225.9496   $225.95   $225.95   $225.90  
  Purchase #5 $6.77   12.294%   $7.6023   $7.60   $7.60   $7.60  
  Purchase #6 $69.64   13.150%   $78.7977   $78.80   $78.80   $78.80  
  Purchase #7 $147.72   13.612%   $167.8276   $167.83   $167.85   $167.80  
  7 purchase totals = $765.81       $848.8378   $848.84   $848.80   $848.80