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 $241.91   7.282%   $259.5259   $259.53   $259.55   $259.50  
  Purchase #2 $114.81   7.450%   $123.3633   $123.36   $123.35   $123.40  
  Purchase #3 $188.27   8.763%   $204.7681   $204.77   $204.75   $204.80  
  Purchase #4 $49.71   10.558%   $54.9584   $54.96   $54.95   $55.00  
  Purchase #5 $96.98   13.785%   $110.3487   $110.35   $110.35   $110.30  
  Purchase #6 $115.66   4.460%   $120.8184   $120.82   $120.80   $120.80  
  Purchase #7 $193.39   4.735%   $202.547   $202.55   $202.55   $202.50  
  7 purchase totals = $1,000.73       $1,076.3298   $1,076.34   $1,076.30   $1,076.30