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 $180.55   10.413%   $199.3507   $199.35   $199.35   $199.40  
  Purchase #2 $240.80   11.165%   $267.6853   $267.69   $267.70   $267.70  
  Purchase #3 $60.88   13.498%   $69.0976   $69.10   $69.10   $69.10  
  Purchase #4 $113.29   4.387%   $118.26   $118.26   $118.25   $118.30  
  Purchase #5 $240.44   5.244%   $253.0487   $253.05   $253.05   $253.00  
  Purchase #6 $42.92   12.428%   $48.2541   $48.25   $48.25   $48.30  
  Purchase #7 $141.97   4.137%   $147.8433   $147.84   $147.85   $147.80  
  7 purchase totals = $1,020.85       $1,103.5397   $1,103.54   $1,103.55   $1,103.60