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 $108.94   8.412%   $118.104   $118.10   $118.10   $118.10  
  Purchase #2 $230.63   6.211%   $244.9544   $244.95   $244.95   $245.00  
  Purchase #3 $53.82   5.672%   $56.8727   $56.87   $56.85   $56.90  
  Purchase #4 $193.25   9.567%   $211.7382   $211.74   $211.75   $211.70  
  Purchase #5 $55.75   9.412%   $60.9972   $61.00   $61.00   $61.00  
  Purchase #6 $136.55   6.629%   $145.6019   $145.60   $145.60   $145.60  
  Purchase #7 $41.39   4.559%   $43.277   $43.28   $43.30   $43.30  
  7 purchase totals = $820.33       $881.5454   $881.54   $881.55   $881.60