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 $248.25   13.633%   $282.0939   $282.09   $282.10   $282.10  
  Purchase #2 $184.50   10.121%   $203.1732   $203.17   $203.15   $203.20  
  Purchase #3 $58.78   3.172%   $60.6445   $60.64   $60.65   $60.60  
  Purchase #4 $24.83   9.447%   $27.1757   $27.18   $27.20   $27.20  
  Purchase #5 $204.75   9.440%   $224.0784   $224.08   $224.10   $224.10  
  Purchase #6 $184.47   9.665%   $202.299   $202.30   $202.30   $202.30  
  Purchase #7 $161.89   5.172%   $170.263   $170.26   $170.25   $170.30  
  7 purchase totals = $1,067.47       $1,169.7277   $1,169.72   $1,169.75   $1,169.80