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 $166.29   6.695%   $177.4231   $177.42   $177.40   $177.40  
  Purchase #2 $211.61   6.254%   $224.8441   $224.84   $224.85   $224.80  
  Purchase #3 $58.43   7.452%   $62.7842   $62.78   $62.80   $62.80  
  Purchase #4 $143.27   9.457%   $156.819   $156.82   $156.80   $156.80  
  Purchase #5 $209.80   4.271%   $218.7606   $218.76   $218.75   $218.80  
  Purchase #6 $117.62   3.202%   $121.3862   $121.39   $121.40   $121.40  
  Purchase #7 $31.84   6.766%   $33.9943   $33.99   $34.00   $34.00  
  7 purchase totals = $938.86       $996.0115   $996.00   $996.00   $996.00