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 $123.59   7.632%   $133.0224   $133.02   $133.00   $133.00  
  Purchase #2 $232.87   3.395%   $240.7759   $240.78   $240.80   $240.80  
  Purchase #3 $10.67   11.109%   $11.8553   $11.86   $11.85   $11.90  
  Purchase #4 $108.33   9.554%   $118.6798   $118.68   $118.70   $118.70  
  Purchase #5 $155.85   12.213%   $174.884   $174.88   $174.90   $174.90  
  Purchase #6 $212.75   7.251%   $228.1765   $228.18   $228.20   $228.20  
  Purchase #7 $54.32   9.719%   $59.5994   $59.60   $59.60   $59.60  
  7 purchase totals = $898.38       $966.9933   $967.00   $967.05   $967.10