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 $183.96   12.112%   $206.2412   $206.24   $206.25   $206.20  
  Purchase #2 $76.38   13.558%   $86.7356   $86.74   $86.75   $86.70  
  Purchase #3 $83.60   12.413%   $93.9773   $93.98   $94.00   $94.00  
  Purchase #4 $53.72   7.505%   $57.7517   $57.75   $57.75   $57.80  
  Purchase #5 $224.57   8.437%   $243.517   $243.52   $243.50   $243.50  
  Purchase #6 $169.96   5.355%   $179.0614   $179.06   $179.05   $179.10  
  Purchase #7 $232.38   6.525%   $247.5428   $247.54   $247.55   $247.50  
  7 purchase totals = $1,024.57       $1,114.8270   $1,114.83   $1,114.85   $1,114.80