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 $98.54   5.255%   $103.7183   $103.72   $103.70   $103.70  
  Purchase #2 $12.74   5.409%   $13.4291   $13.43   $13.45   $13.40  
  Purchase #3 $18.37   7.147%   $19.6829   $19.68   $19.70   $19.70  
  Purchase #4 $55.80   9.336%   $61.0095   $61.01   $61.00   $61.00  
  Purchase #5 $117.41   13.226%   $132.9386   $132.94   $132.95   $132.90  
  Purchase #6 $189.35   9.593%   $207.5143   $207.51   $207.50   $207.50  
  Purchase #7 $220.69   12.715%   $248.7507   $248.75   $248.75   $248.80  
  7 purchase totals = $712.90       $787.0434   $787.04   $787.05   $787.00