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 $92.65   13.237%   $104.9141   $104.91   $104.90   $104.90  
  Purchase #2 $218.49   13.703%   $248.4297   $248.43   $248.45   $248.40  
  Purchase #3 $211.71   12.603%   $238.3918   $238.39   $238.40   $238.40  
  Purchase #4 $98.66   3.679%   $102.2897   $102.29   $102.30   $102.30  
  Purchase #5 $15.57   6.751%   $16.6211   $16.62   $16.60   $16.60  
  Purchase #6 $106.65   3.197%   $110.0596   $110.06   $110.05   $110.10  
  Purchase #7 $196.46   9.254%   $214.6404   $214.64   $214.65   $214.60  
  7 purchase totals = $940.19       $1,035.3464   $1,035.34   $1,035.35   $1,035.30