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 $219.38   5.869%   $232.2554   $232.26   $232.25   $232.30  
  Purchase #2 $201.56   8.546%   $218.7853   $218.79   $218.80   $218.80  
  Purchase #3 $128.42   9.597%   $140.7445   $140.74   $140.75   $140.70  
  Purchase #4 $168.47   6.215%   $178.9404   $178.94   $178.95   $178.90  
  Purchase #5 $194.25   5.779%   $205.4757   $205.48   $205.50   $205.50  
  Purchase #6 $71.48   6.821%   $76.3557   $76.36   $76.35   $76.40  
  Purchase #7 $230.33   5.513%   $243.0281   $243.03   $243.05   $243.00  
  7 purchase totals = $1,213.89       $1,295.5851   $1,295.60   $1,295.65   $1,295.60