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 $158.31   13.231%   $179.256   $179.26   $179.25   $179.30  
  Purchase #2 $53.32   3.343%   $55.1025   $55.10   $55.10   $55.10  
  Purchase #3 $104.92   5.587%   $110.7819   $110.78   $110.80   $110.80  
  Purchase #4 $209.61   5.352%   $220.8283   $220.83   $220.85   $220.80  
  Purchase #5 $184.30   4.811%   $193.1667   $193.17   $193.15   $193.20  
  Purchase #6 $244.86   7.780%   $263.9101   $263.91   $263.90   $263.90  
  Purchase #7 $21.85   13.515%   $24.803   $24.80   $24.80   $24.80  
  7 purchase totals = $977.17       $1,047.8485   $1,047.85   $1,047.85   $1,047.90