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 $226.93   10.847%   $251.5451   $251.55   $251.55   $251.50  
  Purchase #2 $67.52   8.556%   $73.297   $73.30   $73.30   $73.30  
  Purchase #3 $30.75   4.402%   $32.1036   $32.10   $32.10   $32.10  
  Purchase #4 $172.31   7.535%   $185.2936   $185.29   $185.30   $185.30  
  Purchase #5 $73.41   10.474%   $81.099   $81.10   $81.10   $81.10  
  Purchase #6 $87.46   12.408%   $98.312   $98.31   $98.30   $98.30  
  Purchase #7 $250.49   10.594%   $277.0269   $277.03   $277.05   $277.00  
  7 purchase totals = $908.87       $998.6772   $998.68   $998.70   $998.60