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 $186.97   8.414%   $202.7017   $202.70   $202.70   $202.70  
  Purchase #2 $247.83   3.156%   $255.6515   $255.65   $255.65   $255.70  
  Purchase #3 $53.92   9.173%   $58.8661   $58.87   $58.85   $58.90  
  Purchase #4 $86.57   7.320%   $92.9069   $92.91   $92.90   $92.90  
  Purchase #5 $106.74   8.151%   $115.4404   $115.44   $115.45   $115.40  
  Purchase #6 $225.68   6.444%   $240.2228   $240.22   $240.20   $240.20  
  Purchase #7 $104.44   12.802%   $117.8104   $117.81   $117.80   $117.80  
  7 purchase totals = $1,012.15       $1,083.5998   $1,083.60   $1,083.55   $1,083.60