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 $106.66   12.460%   $119.9498   $119.95   $119.95   $119.90  
  Purchase #2 $225.61   13.514%   $256.0989   $256.10   $256.10   $256.10  
  Purchase #3 $121.82   13.709%   $138.5203   $138.52   $138.50   $138.50  
  Purchase #4 $85.60   3.388%   $88.5001   $88.50   $88.50   $88.50  
  Purchase #5 $208.30   11.221%   $231.6733   $231.67   $231.65   $231.70  
  Purchase #6 $141.49   13.834%   $161.0637   $161.06   $161.05   $161.10  
  Purchase #7 $64.67   12.828%   $72.9659   $72.97   $72.95   $73.00  
  7 purchase totals = $954.15       $1,068.7720   $1,068.77   $1,068.70   $1,068.80