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 $55.82   8.411%   $60.515   $60.52   $60.50   $60.50  
  Purchase #2 $113.83   7.849%   $122.7645   $122.76   $122.75   $122.80  
  Purchase #3 $156.41   4.589%   $163.5877   $163.59   $163.60   $163.60  
  Purchase #4 $155.85   6.286%   $165.6467   $165.65   $165.65   $165.60  
  Purchase #5 $41.38   3.106%   $42.6653   $42.67   $42.65   $42.70  
  Purchase #6 $92.42   4.809%   $96.8645   $96.86   $96.85   $96.90  
  Purchase #7 $190.69   7.594%   $205.171   $205.17   $205.15   $205.20  
  7 purchase totals = $806.40       $857.2147   $857.22   $857.15   $857.30