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 $211.29   8.818%   $229.9216   $229.92   $229.90   $229.90  
  Purchase #2 $158.86   4.272%   $165.6465   $165.65   $165.65   $165.60  
  Purchase #3 $174.56   4.436%   $182.3035   $182.30   $182.30   $182.30  
  Purchase #4 $99.53   9.431%   $108.9167   $108.92   $108.90   $108.90  
  Purchase #5 $15.53   6.156%   $16.486   $16.49   $16.50   $16.50  
  Purchase #6 $179.56   7.781%   $193.5316   $193.53   $193.55   $193.50  
  Purchase #7 $103.88   13.736%   $118.149   $118.15   $118.15   $118.10  
  7 purchase totals = $943.21       $1,014.9549   $1,014.96   $1,014.95   $1,014.80