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 $184.87   5.395%   $194.8437   $194.84   $194.85   $194.80  
  Purchase #2 $240.73   9.120%   $262.6846   $262.68   $262.70   $262.70  
  Purchase #3 $151.62   9.458%   $165.9602   $165.96   $165.95   $166.00  
  Purchase #4 $182.97   13.128%   $206.9903   $206.99   $207.00   $207.00  
  Purchase #5 $230.29   12.472%   $259.0118   $259.01   $259.00   $259.00  
  Purchase #6 $36.41   8.496%   $39.5034   $39.50   $39.50   $39.50  
  Purchase #7 $60.72   5.735%   $64.2023   $64.20   $64.20   $64.20  
  7 purchase totals = $1,087.61       $1,193.1963   $1,193.18   $1,193.20   $1,193.20