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 $184.66   10.734%   $204.4814   $204.48   $204.50   $204.50  
  Purchase #2 $148.83   13.374%   $168.7345   $168.73   $168.75   $168.70  
  Purchase #3 $127.44   3.717%   $132.1769   $132.18   $132.20   $132.20  
  Purchase #4 $186.26   5.769%   $197.0053   $197.01   $197.00   $197.00  
  Purchase #5 $68.94   9.533%   $75.5121   $75.51   $75.50   $75.50  
  Purchase #6 $87.45   6.370%   $93.0206   $93.02   $93.00   $93.00  
  Purchase #7 $165.99   12.489%   $186.7205   $186.72   $186.70   $186.70  
  7 purchase totals = $969.57       $1,057.6513   $1,057.65   $1,057.65   $1,057.60