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 $133.47   12.610%   $150.3006   $150.30   $150.30   $150.30  
  Purchase #2 $207.46   13.234%   $234.9153   $234.92   $234.90   $234.90  
  Purchase #3 $202.45   10.714%   $224.1405   $224.14   $224.15   $224.10  
  Purchase #4 $56.55   3.793%   $58.6949   $58.69   $58.70   $58.70  
  Purchase #5 $131.28   9.757%   $144.089   $144.09   $144.10   $144.10  
  Purchase #6 $179.70   12.811%   $202.7214   $202.72   $202.70   $202.70  
  Purchase #7 $36.89   6.435%   $39.2639   $39.26   $39.25   $39.30  
  7 purchase totals = $947.80       $1,054.1256   $1,054.12   $1,054.10   $1,054.10