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 $167.52   10.190%   $184.5903   $184.59   $184.60   $184.60  
  Purchase #2 $206.73   9.531%   $226.4334   $226.43   $226.45   $226.40  
  Purchase #3 $118.90   3.279%   $122.7987   $122.80   $122.80   $122.80  
  Purchase #4 $235.32   4.272%   $245.3729   $245.37   $245.35   $245.40  
  Purchase #5 $135.68   10.396%   $149.7853   $149.79   $149.80   $149.80  
  Purchase #6 $167.99   4.157%   $174.9733   $174.97   $174.95   $175.00  
  Purchase #7 $86.86   7.412%   $93.2981   $93.30   $93.30   $93.30  
  7 purchase totals = $1,119.00       $1,197.2520   $1,197.25   $1,197.25   $1,197.30