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 $86.69   11.113%   $96.3239   $96.32   $96.30   $96.30  
  Purchase #2 $54.80   3.588%   $56.7662   $56.77   $56.75   $56.80  
  Purchase #3 $22.60   11.744%   $25.2541   $25.25   $25.25   $25.30  
  Purchase #4 $240.47   7.511%   $258.5317   $258.53   $258.55   $258.50  
  Purchase #5 $211.32   5.700%   $223.3652   $223.37   $223.35   $223.40  
  Purchase #6 $199.30   10.107%   $219.4433   $219.44   $219.45   $219.40  
  Purchase #7 $111.33   4.135%   $115.9335   $115.93   $115.95   $115.90  
  7 purchase totals = $926.51       $995.6179   $995.61   $995.60   $995.60