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 $11.45   3.417%   $11.8412   $11.84   $11.85   $11.80  
  Purchase #2 $12.36   13.421%   $14.0188   $14.02   $14.00   $14.00  
  Purchase #3 $159.27   5.123%   $167.4294   $167.43   $167.45   $167.40  
  Purchase #4 $185.69   6.161%   $197.1304   $197.13   $197.15   $197.10  
  Purchase #5 $242.85   6.222%   $257.9601   $257.96   $257.95   $258.00  
  Purchase #6 $179.81   3.127%   $185.4327   $185.43   $185.45   $185.40  
  Purchase #7 $189.51   6.616%   $202.048   $202.05   $202.05   $202.00  
  7 purchase totals = $980.94       $1,035.8606   $1,035.86   $1,035.90   $1,035.70