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 $234.39   8.567%   $254.4702   $254.47   $254.45   $254.50  
  Purchase #2 $70.86   6.367%   $75.3717   $75.37   $75.35   $75.40  
  Purchase #3 $179.61   9.349%   $196.4017   $196.40   $196.40   $196.40  
  Purchase #4 $154.32   10.479%   $170.4912   $170.49   $170.50   $170.50  
  Purchase #5 $119.96   6.694%   $127.9901   $127.99   $128.00   $128.00  
  Purchase #6 $122.98   11.253%   $136.8189   $136.82   $136.80   $136.80  
  Purchase #7 $184.40   9.119%   $201.2154   $201.22   $201.20   $201.20  
  7 purchase totals = $1,066.52       $1,162.7592   $1,162.76   $1,162.70   $1,162.80