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 $56.98   8.120%   $61.6068   $61.61   $61.60   $61.60  
  Purchase #2 $110.47   8.307%   $119.6467   $119.65   $119.65   $119.60  
  Purchase #3 $241.47   9.174%   $263.6225   $263.62   $263.60   $263.60  
  Purchase #4 $223.58   12.472%   $251.4649   $251.46   $251.45   $251.50  
  Purchase #5 $145.63   11.203%   $161.9449   $161.94   $161.95   $161.90  
  Purchase #6 $51.51   12.668%   $58.0353   $58.04   $58.05   $58.00  
  Purchase #7 $88.27   10.873%   $97.8676   $97.87   $97.85   $97.90  
  7 purchase totals = $917.91       $1,014.1887   $1,014.19   $1,014.15   $1,014.10