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 $69.76   10.873%   $77.345   $77.35   $77.35   $77.30  
  Purchase #2 $170.25   12.749%   $191.9552   $191.96   $191.95   $192.00  
  Purchase #3 $49.33   3.614%   $51.1128   $51.11   $51.10   $51.10  
  Purchase #4 $117.86   10.787%   $130.5736   $130.57   $130.55   $130.60  
  Purchase #5 $203.41   4.328%   $212.2136   $212.21   $212.20   $212.20  
  Purchase #6 $18.51   12.820%   $20.883   $20.88   $20.90   $20.90  
  Purchase #7 $80.84   6.119%   $85.7866   $85.79   $85.80   $85.80  
  7 purchase totals = $709.96       $769.8698   $769.87   $769.85   $769.90