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 $235.60   13.578%   $267.5898   $267.59   $267.60   $267.60  
  Purchase #2 $132.33   5.290%   $139.3303   $139.33   $139.35   $139.30  
  Purchase #3 $141.37   6.278%   $150.2452   $150.25   $150.25   $150.20  
  Purchase #4 $13.47   8.764%   $14.6505   $14.65   $14.65   $14.70  
  Purchase #5 $82.83   10.222%   $91.2969   $91.30   $91.30   $91.30  
  Purchase #6 $45.64   4.467%   $47.6787   $47.68   $47.70   $47.70  
  Purchase #7 $150.62   8.444%   $163.3384   $163.34   $163.35   $163.30  
  7 purchase totals = $801.86       $874.1298   $874.14   $874.20   $874.10