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 $218.29   6.522%   $232.5269   $232.53   $232.55   $232.50  
  Purchase #2 $56.87   7.603%   $61.1938   $61.19   $61.20   $61.20  
  Purchase #3 $11.95   11.625%   $13.3392   $13.34   $13.35   $13.30  
  Purchase #4 $219.39   13.347%   $248.672   $248.67   $248.65   $248.70  
  Purchase #5 $75.36   10.823%   $83.5162   $83.52   $83.50   $83.50  
  Purchase #6 $178.94   3.739%   $185.6306   $185.63   $185.65   $185.60  
  Purchase #7 $205.28   12.587%   $231.1186   $231.12   $231.10   $231.10  
  7 purchase totals = $966.08       $1,055.9973   $1,056.00   $1,056.00   $1,055.90