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 $175.73   12.367%   $197.4625   $197.46   $197.45   $197.50  
  Purchase #2 $207.58   8.318%   $224.8465   $224.85   $224.85   $224.80  
  Purchase #3 $184.37   11.566%   $205.6942   $205.69   $205.70   $205.70  
  Purchase #4 $152.69   6.472%   $162.5721   $162.57   $162.55   $162.60  
  Purchase #5 $19.30   5.362%   $20.3349   $20.33   $20.35   $20.30  
  Purchase #6 $133.58   5.438%   $140.8441   $140.84   $140.85   $140.80  
  Purchase #7 $120.85   11.148%   $134.3224   $134.32   $134.30   $134.30  
  7 purchase totals = $994.10       $1,086.0767   $1,086.06   $1,086.05   $1,086.00