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 $76.60   13.604%   $87.0207   $87.02   $87.00   $87.00  
  Purchase #2 $189.86   10.356%   $209.5219   $209.52   $209.50   $209.50  
  Purchase #3 $106.52   7.520%   $114.5303   $114.53   $114.55   $114.50  
  Purchase #4 $92.84   6.312%   $98.7001   $98.70   $98.70   $98.70  
  Purchase #5 $182.26   12.408%   $204.8748   $204.87   $204.85   $204.90  
  Purchase #6 $143.54   11.775%   $160.4418   $160.44   $160.45   $160.40  
  Purchase #7 $149.73   5.250%   $157.5908   $157.59   $157.60   $157.60  
  7 purchase totals = $941.35       $1,032.6804   $1,032.67   $1,032.65   $1,032.60