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 $229.97   7.295%   $246.7463   $246.75   $246.75   $246.70  
  Purchase #2 $41.56   13.359%   $47.112   $47.11   $47.10   $47.10  
  Purchase #3 $37.54   3.131%   $38.7154   $38.72   $38.70   $38.70  
  Purchase #4 $81.66   12.154%   $91.585   $91.59   $91.60   $91.60  
  Purchase #5 $245.61   9.546%   $269.0559   $269.06   $269.05   $269.10  
  Purchase #6 $243.34   4.490%   $254.266   $254.27   $254.25   $254.30  
  Purchase #7 $138.97   12.853%   $156.8318   $156.83   $156.85   $156.80  
  7 purchase totals = $1,018.65       $1,104.3124   $1,104.33   $1,104.30   $1,104.30