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 $82.81   12.333%   $93.023   $93.02   $93.00   $93.00  
  Purchase #2 $185.72   10.791%   $205.761   $205.76   $205.75   $205.80  
  Purchase #3 $113.89   12.652%   $128.2994   $128.30   $128.30   $128.30  
  Purchase #4 $162.29   12.739%   $182.9641   $182.96   $182.95   $183.00  
  Purchase #5 $187.39   13.372%   $212.4478   $212.45   $212.45   $212.40  
  Purchase #6 $189.99   6.314%   $201.986   $201.99   $202.00   $202.00  
  Purchase #7 $137.43   5.633%   $145.1714   $145.17   $145.15   $145.20  
  7 purchase totals = $1,059.52       $1,169.6527   $1,169.65   $1,169.60   $1,169.70