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 $75.69   11.745%   $84.5798   $84.58   $84.60   $84.60  
  Purchase #2 $155.52   7.272%   $166.8294   $166.83   $166.85   $166.80  
  Purchase #3 $250.74   5.214%   $263.8136   $263.81   $263.80   $263.80  
  Purchase #4 $205.53   5.715%   $217.276   $217.28   $217.30   $217.30  
  Purchase #5 $31.53   9.302%   $34.4629   $34.46   $34.45   $34.50  
  Purchase #6 $100.67   6.133%   $106.8441   $106.84   $106.85   $106.80  
  Purchase #7 $150.25   7.367%   $161.3189   $161.32   $161.30   $161.30  
  7 purchase totals = $969.93       $1,035.1247   $1,035.12   $1,035.15   $1,035.10