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 $216.29   12.511%   $243.35   $243.35   $243.35   $243.40  
  Purchase #2 $59.76   10.357%   $65.9493   $65.95   $65.95   $65.90  
  Purchase #3 $230.95   8.135%   $249.7378   $249.74   $249.75   $249.70  
  Purchase #4 $72.37   12.561%   $81.4604   $81.46   $81.45   $81.50  
  Purchase #5 $11.33   8.288%   $12.269   $12.27   $12.25   $12.30  
  Purchase #6 $140.89   10.404%   $155.5482   $155.55   $155.55   $155.50  
  Purchase #7 $192.92   9.206%   $210.6802   $210.68   $210.70   $210.70  
  7 purchase totals = $924.51       $1,018.9949   $1,019.00   $1,019.00   $1,019.00