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 $202.53   12.873%   $228.6017   $228.60   $228.60   $228.60  
  Purchase #2 $29.54   10.322%   $32.5891   $32.59   $32.60   $32.60  
  Purchase #3 $234.67   11.109%   $260.7395   $260.74   $260.75   $260.70  
  Purchase #4 $165.28   9.595%   $181.1386   $181.14   $181.15   $181.10  
  Purchase #5 $177.98   9.147%   $194.2598   $194.26   $194.25   $194.30  
  Purchase #6 $241.25   6.803%   $257.6622   $257.66   $257.65   $257.70  
  Purchase #7 $9.80   7.239%   $10.5094   $10.51   $10.50   $10.50  
  7 purchase totals = $1,061.05       $1,165.5003   $1,165.50   $1,165.50   $1,165.50