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 $218.71   12.471%   $245.9853   $245.99   $246.00   $246.00  
  Purchase #2 $183.72   4.266%   $191.5575   $191.56   $191.55   $191.60  
  Purchase #3 $167.42   12.168%   $187.7917   $187.79   $187.80   $187.80  
  Purchase #4 $25.73   10.303%   $28.381   $28.38   $28.40   $28.40  
  Purchase #5 $28.69   11.481%   $31.9839   $31.98   $32.00   $32.00  
  Purchase #6 $138.66   4.563%   $144.9871   $144.99   $145.00   $145.00  
  Purchase #7 $126.81   6.751%   $135.3709   $135.37   $135.35   $135.40  
  7 purchase totals = $889.74       $966.0574   $966.06   $966.10   $966.20