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 $90.27   12.427%   $101.4879   $101.49   $101.50   $101.50  
  Purchase #2 $178.80   12.793%   $201.6739   $201.67   $201.65   $201.70  
  Purchase #3 $65.65   10.160%   $72.32   $72.32   $72.30   $72.30  
  Purchase #4 $56.74   12.112%   $63.6123   $63.61   $63.60   $63.60  
  Purchase #5 $228.30   5.410%   $240.651   $240.65   $240.65   $240.70  
  Purchase #6 $102.87   4.215%   $107.206   $107.21   $107.20   $107.20  
  Purchase #7 $154.92   8.473%   $168.0464   $168.05   $168.05   $168.00  
  7 purchase totals = $877.55       $954.9975   $955.00   $954.95   $955.00