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 $155.81   6.819%   $166.4347   $166.43   $166.45   $166.40  
  Purchase #2 $67.85   4.571%   $70.9514   $70.95   $70.95   $71.00  
  Purchase #3 $185.35   6.321%   $197.066   $197.07   $197.05   $197.10  
  Purchase #4 $214.98   13.145%   $243.2391   $243.24   $243.25   $243.20  
  Purchase #5 $167.37   4.212%   $174.4196   $174.42   $174.40   $174.40  
  Purchase #6 $60.30   12.765%   $67.9973   $68.00   $68.00   $68.00  
  Purchase #7 $125.34   4.216%   $130.6243   $130.62   $130.60   $130.60  
  7 purchase totals = $977.00       $1,050.7324   $1,050.73   $1,050.70   $1,050.70