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 $46.51   8.791%   $50.5987   $50.60   $50.60   $50.60  
  Purchase #2 $185.27   9.510%   $202.8892   $202.89   $202.90   $202.90  
  Purchase #3 $131.66   7.751%   $141.865   $141.87   $141.85   $141.90  
  Purchase #4 $230.39   4.808%   $241.4672   $241.47   $241.45   $241.50  
  Purchase #5 $175.50   6.676%   $187.2164   $187.22   $187.20   $187.20  
  Purchase #6 $232.27   11.429%   $258.8161   $258.82   $258.80   $258.80  
  Purchase #7 $39.48   10.276%   $43.537   $43.54   $43.55   $43.50  
  7 purchase totals = $1,041.08       $1,126.3896   $1,126.41   $1,126.35   $1,126.40