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 $62.73   4.687%   $65.6702   $65.67   $65.65   $65.70  
  Purchase #2 $250.69   10.297%   $276.5035   $276.50   $276.50   $276.50  
  Purchase #3 $37.44   11.616%   $41.789   $41.79   $41.80   $41.80  
  Purchase #4 $197.54   8.372%   $214.078   $214.08   $214.10   $214.10  
  Purchase #5 $181.71   9.289%   $198.589   $198.59   $198.60   $198.60  
  Purchase #6 $109.79   11.241%   $122.1315   $122.13   $122.15   $122.10  
  Purchase #7 $21.89   9.728%   $24.0195   $24.02   $24.00   $24.00  
  7 purchase totals = $861.79       $942.7807   $942.78   $942.80   $942.80