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 $23.39   12.764%   $26.3755   $26.38   $26.40   $26.40  
  Purchase #2 $245.61   3.475%   $254.1449   $254.14   $254.15   $254.10  
  Purchase #3 $233.55   4.277%   $243.5389   $243.54   $243.55   $243.50  
  Purchase #4 $27.65   3.835%   $28.7104   $28.71   $28.70   $28.70  
  Purchase #5 $191.65   6.726%   $204.5404   $204.54   $204.55   $204.50  
  Purchase #6 $211.87   8.415%   $229.6989   $229.70   $229.70   $229.70  
  Purchase #7 $61.66   6.477%   $65.6537   $65.65   $65.65   $65.70  
  7 purchase totals = $995.38       $1,052.6627   $1,052.66   $1,052.70   $1,052.60