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 $74.39   11.475%   $82.9263   $82.93   $82.95   $82.90  
  Purchase #2 $219.44   4.281%   $228.8342   $228.83   $228.85   $228.80  
  Purchase #3 $190.76   5.715%   $201.6619   $201.66   $201.65   $201.70  
  Purchase #4 $125.44   11.132%   $139.404   $139.40   $139.40   $139.40  
  Purchase #5 $228.31   11.705%   $255.0337   $255.03   $255.05   $255.00  
  Purchase #6 $44.66   11.786%   $49.9236   $49.92   $49.90   $49.90  
  Purchase #7 $91.53   7.784%   $98.6547   $98.65   $98.65   $98.70  
  7 purchase totals = $974.53       $1,056.4384   $1,056.42   $1,056.45   $1,056.40