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 $176.91   13.844%   $201.4014   $201.40   $201.40   $201.40  
  Purchase #2 $58.53   6.122%   $62.1132   $62.11   $62.10   $62.10  
  Purchase #3 $48.65   8.131%   $52.6057   $52.61   $52.60   $52.60  
  Purchase #4 $237.41   6.228%   $252.1959   $252.20   $252.20   $252.20  
  Purchase #5 $171.95   3.559%   $178.0697   $178.07   $178.05   $178.10  
  Purchase #6 $80.54   8.132%   $87.0895   $87.09   $87.10   $87.10  
  Purchase #7 $198.59   10.490%   $219.4221   $219.42   $219.40   $219.40  
  7 purchase totals = $972.58       $1,052.8975   $1,052.90   $1,052.85   $1,052.90