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 $242.98   13.807%   $276.5282   $276.53   $276.55   $276.50  
  Purchase #2 $168.53   10.198%   $185.7167   $185.72   $185.70   $185.70  
  Purchase #3 $210.98   8.391%   $228.6833   $228.68   $228.70   $228.70  
  Purchase #4 $225.79   11.577%   $251.9297   $251.93   $251.95   $251.90  
  Purchase #5 $39.29   12.139%   $44.0594   $44.06   $44.05   $44.10  
  Purchase #6 $124.65   10.841%   $138.1633   $138.16   $138.15   $138.20  
  Purchase #7 $108.65   11.303%   $120.9307   $120.93   $120.95   $120.90  
  7 purchase totals = $1,120.87       $1,246.0113   $1,246.01   $1,246.05   $1,246.00