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 $34.68   6.253%   $36.8485   $36.85   $36.85   $36.80  
  Purchase #2 $232.74   3.778%   $241.5329   $241.53   $241.55   $241.50  
  Purchase #3 $168.58   6.613%   $179.7282   $179.73   $179.75   $179.70  
  Purchase #4 $127.86   8.688%   $138.9685   $138.97   $138.95   $139.00  
  Purchase #5 $90.52   6.426%   $96.3368   $96.34   $96.35   $96.30  
  Purchase #6 $157.94   9.381%   $172.7564   $172.76   $172.75   $172.80  
  Purchase #7 $134.84   10.114%   $148.4777   $148.48   $148.50   $148.50  
  7 purchase totals = $947.16       $1,014.6490   $1,014.66   $1,014.70   $1,014.60