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 $67.45   4.606%   $70.5567   $70.56   $70.55   $70.60  
  Purchase #2 $120.32   4.818%   $126.117   $126.12   $126.10   $126.10  
  Purchase #3 $58.47   5.811%   $61.8677   $61.87   $61.85   $61.90  
  Purchase #4 $220.89   13.311%   $250.2927   $250.29   $250.30   $250.30  
  Purchase #5 $98.80   6.173%   $104.8989   $104.90   $104.90   $104.90  
  Purchase #6 $126.42   5.377%   $133.2176   $133.22   $133.20   $133.20  
  Purchase #7 $244.73   3.539%   $253.391   $253.39   $253.40   $253.40  
  7 purchase totals = $937.08       $1,000.3416   $1,000.35   $1,000.30   $1,000.40