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 $69.75   10.871%   $77.3325   $77.33   $77.35   $77.30  
  Purchase #2 $21.49   5.541%   $22.6808   $22.68   $22.70   $22.70  
  Purchase #3 $214.27   12.656%   $241.388   $241.39   $241.40   $241.40  
  Purchase #4 $133.94   6.737%   $142.9635   $142.96   $142.95   $143.00  
  Purchase #5 $181.80   4.122%   $189.2938   $189.29   $189.30   $189.30  
  Purchase #6 $119.48   11.313%   $132.9968   $133.00   $133.00   $133.00  
  Purchase #7 $138.48   12.384%   $155.6294   $155.63   $155.65   $155.60  
  7 purchase totals = $879.21       $962.2848   $962.28   $962.35   $962.30