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 $58.71   9.483%   $64.2775   $64.28   $64.30   $64.30  
  Purchase #2 $221.29   4.315%   $230.8387   $230.84   $230.85   $230.80  
  Purchase #3 $165.81   6.338%   $176.319   $176.32   $176.30   $176.30  
  Purchase #4 $82.62   13.276%   $93.5886   $93.59   $93.60   $93.60  
  Purchase #5 $130.29   11.282%   $144.9893   $144.99   $145.00   $145.00  
  Purchase #6 $17.59   9.402%   $19.2438   $19.24   $19.25   $19.20  
  Purchase #7 $51.87   9.188%   $56.6358   $56.64   $56.65   $56.60  
  7 purchase totals = $728.18       $785.8927   $785.90   $785.95   $785.80