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 $232.52   13.681%   $264.3311   $264.33   $264.35   $264.30  
  Purchase #2 $33.31   9.562%   $36.4951   $36.50   $36.50   $36.50  
  Purchase #3 $190.40   6.549%   $202.8693   $202.87   $202.85   $202.90  
  Purchase #4 $13.49   5.444%   $14.2244   $14.22   $14.20   $14.20  
  Purchase #5 $14.60   5.511%   $15.4046   $15.40   $15.40   $15.40  
  Purchase #6 $153.40   7.744%   $165.2793   $165.28   $165.30   $165.30  
  Purchase #7 $67.94   9.566%   $74.4391   $74.44   $74.45   $74.40  
  7 purchase totals = $705.66       $773.0429   $773.04   $773.05   $773.00