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 $88.54   7.107%   $94.8325   $94.83   $94.85   $94.80  
  Purchase #2 $55.73   7.452%   $59.883   $59.88   $59.90   $59.90  
  Purchase #3 $53.68   8.232%   $58.0989   $58.10   $58.10   $58.10  
  Purchase #4 $90.25   4.201%   $94.0414   $94.04   $94.05   $94.00  
  Purchase #5 $155.82   10.662%   $172.4335   $172.43   $172.45   $172.40  
  Purchase #6 $187.70   4.609%   $196.3511   $196.35   $196.35   $196.40  
  Purchase #7 $189.49   9.462%   $207.4195   $207.42   $207.40   $207.40  
  7 purchase totals = $821.21       $883.0599   $883.05   $883.10   $883.00