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 $188.93   8.104%   $204.2409   $204.24   $204.25   $204.20  
  Purchase #2 $91.93   4.681%   $96.2332   $96.23   $96.25   $96.20  
  Purchase #3 $64.48   3.413%   $66.6807   $66.68   $66.70   $66.70  
  Purchase #4 $184.99   4.443%   $193.2091   $193.21   $193.20   $193.20  
  Purchase #5 $225.86   3.482%   $233.7244   $233.72   $233.70   $233.70  
  Purchase #6 $206.50   3.390%   $213.5004   $213.50   $213.50   $213.50  
  Purchase #7 $115.85   12.666%   $130.5236   $130.52   $130.50   $130.50  
  7 purchase totals = $1,078.54       $1,138.1123   $1,138.10   $1,138.10   $1,138.00