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 $53.49   8.161%   $57.8553   $57.86   $57.85   $57.90  
  Purchase #2 $69.60   10.672%   $77.0277   $77.03   $77.05   $77.00  
  Purchase #3 $148.79   4.731%   $155.8293   $155.83   $155.85   $155.80  
  Purchase #4 $241.84   10.534%   $267.3154   $267.32   $267.30   $267.30  
  Purchase #5 $26.26   13.615%   $29.8353   $29.84   $29.85   $29.80  
  Purchase #6 $167.28   9.709%   $183.5212   $183.52   $183.50   $183.50  
  Purchase #7 $230.93   8.448%   $250.439   $250.44   $250.45   $250.40  
  7 purchase totals = $938.19       $1,021.8232   $1,021.84   $1,021.85   $1,021.70