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 $88.54   7.595%   $95.2646   $95.26   $95.25   $95.30  
  Purchase #2 $159.68   3.611%   $165.446   $165.45   $165.45   $165.40  
  Purchase #3 $28.53   12.600%   $32.1248   $32.12   $32.10   $32.10  
  Purchase #4 $238.54   13.172%   $269.9605   $269.96   $269.95   $270.00  
  Purchase #5 $49.49   6.779%   $52.8449   $52.84   $52.85   $52.80  
  Purchase #6 $120.99   9.540%   $132.5324   $132.53   $132.55   $132.50  
  Purchase #7 $63.74   3.394%   $65.9033   $65.90   $65.90   $65.90  
  7 purchase totals = $749.51       $814.0765   $814.06   $814.05   $814.00