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 $88.59   5.592%   $93.544   $93.54   $93.55   $93.50  
  Purchase #2 $172.77   4.396%   $180.365   $180.37   $180.35   $180.40  
  Purchase #3 $45.91   6.374%   $48.8363   $48.84   $48.85   $48.80  
  Purchase #4 $43.84   8.439%   $47.5397   $47.54   $47.55   $47.50  
  Purchase #5 $32.96   13.393%   $37.3743   $37.37   $37.35   $37.40  
  Purchase #6 $155.60   6.825%   $166.2197   $166.22   $166.20   $166.20  
  Purchase #7 $244.98   11.544%   $273.2605   $273.26   $273.25   $273.30  
  7 purchase totals = $784.65       $847.1395   $847.14   $847.10   $847.10