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 $246.97   11.454%   $275.2579   $275.26   $275.25   $275.30  
  Purchase #2 $172.26   13.109%   $194.8416   $194.84   $194.85   $194.80  
  Purchase #3 $107.69   10.467%   $118.9619   $118.96   $118.95   $119.00  
  Purchase #4 $31.44   12.425%   $35.3464   $35.35   $35.35   $35.30  
  Purchase #5 $119.27   9.719%   $130.8619   $130.86   $130.85   $130.90  
  Purchase #6 $116.41   8.740%   $126.5842   $126.58   $126.60   $126.60  
  Purchase #7 $141.84   10.462%   $156.6793   $156.68   $156.70   $156.70  
  7 purchase totals = $935.88       $1,038.5332   $1,038.53   $1,038.55   $1,038.60