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 $116.90   13.776%   $133.0041   $133.00   $133.00   $133.00  
  Purchase #2 $186.31   7.873%   $200.9782   $200.98   $201.00   $201.00  
  Purchase #3 $142.98   8.249%   $154.7744   $154.77   $154.75   $154.80  
  Purchase #4 $106.78   4.137%   $111.1975   $111.20   $111.20   $111.20  
  Purchase #5 $250.95   5.466%   $264.6669   $264.67   $264.65   $264.70  
  Purchase #6 $242.85   7.350%   $260.6995   $260.70   $260.70   $260.70  
  Purchase #7 $55.70   10.354%   $61.4672   $61.47   $61.45   $61.50  
  7 purchase totals = $1,102.47       $1,186.7878   $1,186.79   $1,186.75   $1,186.90