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 $68.92   9.705%   $75.6087   $75.61   $75.60   $75.60  
  Purchase #2 $103.39   5.226%   $108.7932   $108.79   $108.80   $108.80  
  Purchase #3 $250.65   12.195%   $281.2168   $281.22   $281.20   $281.20  
  Purchase #4 $249.93   13.223%   $282.9782   $282.98   $283.00   $283.00  
  Purchase #5 $52.43   7.108%   $56.1567   $56.16   $56.15   $56.20  
  Purchase #6 $188.56   10.230%   $207.8497   $207.85   $207.85   $207.80  
  Purchase #7 $167.60   9.387%   $183.3326   $183.33   $183.35   $183.30  
  7 purchase totals = $1,081.48       $1,195.9359   $1,195.94   $1,195.95   $1,195.90