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 $204.93   6.241%   $217.7197   $217.72   $217.70   $217.70  
  Purchase #2 $32.76   3.408%   $33.8765   $33.88   $33.90   $33.90  
  Purchase #3 $143.55   4.121%   $149.4657   $149.47   $149.45   $149.50  
  Purchase #4 $87.91   10.711%   $97.326   $97.33   $97.35   $97.30  
  Purchase #5 $243.81   10.270%   $268.8493   $268.85   $268.85   $268.80  
  Purchase #6 $128.57   11.429%   $143.2643   $143.26   $143.25   $143.30  
  Purchase #7 $159.72   8.128%   $172.702   $172.70   $172.70   $172.70  
  7 purchase totals = $1,001.25       $1,083.2035   $1,083.21   $1,083.20   $1,083.20