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 $95.25   8.846%   $103.6758   $103.68   $103.70   $103.70  
  Purchase #2 $181.40   10.667%   $200.7499   $200.75   $200.75   $200.70  
  Purchase #3 $108.29   10.363%   $119.5121   $119.51   $119.50   $119.50  
  Purchase #4 $233.96   5.874%   $247.7028   $247.70   $247.70   $247.70  
  Purchase #5 $126.91   6.334%   $134.9485   $134.95   $134.95   $134.90  
  Purchase #6 $96.42   12.673%   $108.6393   $108.64   $108.65   $108.60  
  Purchase #7 $172.78   3.706%   $179.1832   $179.18   $179.20   $179.20  
  7 purchase totals = $1,015.01       $1,094.4116   $1,094.41   $1,094.45   $1,094.30