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 $82.85   3.781%   $85.9826   $85.98   $86.00   $86.00  
  Purchase #2 $186.35   6.243%   $197.9838   $197.98   $198.00   $198.00  
  Purchase #3 $55.73   12.222%   $62.5413   $62.54   $62.55   $62.50  
  Purchase #4 $148.37   9.318%   $162.1951   $162.20   $162.20   $162.20  
  Purchase #5 $53.38   11.591%   $59.5673   $59.57   $59.55   $59.60  
  Purchase #6 $44.38   4.305%   $46.2906   $46.29   $46.30   $46.30  
  Purchase #7 $160.67   12.552%   $180.8373   $180.84   $180.85   $180.80  
  7 purchase totals = $731.73       $795.3980   $795.40   $795.45   $795.40