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 $85.95   10.287%   $94.7917   $94.79   $94.80   $94.80  
  Purchase #2 $242.46   5.678%   $256.2269   $256.23   $256.25   $256.20  
  Purchase #3 $179.31   5.194%   $188.6234   $188.62   $188.60   $188.60  
  Purchase #4 $124.45   10.370%   $137.3555   $137.36   $137.35   $137.40  
  Purchase #5 $194.34   3.284%   $200.7221   $200.72   $200.70   $200.70  
  Purchase #6 $102.83   3.546%   $106.4764   $106.48   $106.50   $106.50  
  Purchase #7 $174.69   3.628%   $181.0278   $181.03   $181.05   $181.00  
  7 purchase totals = $1,104.03       $1,165.2238   $1,165.23   $1,165.25   $1,165.20