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 $116.66   6.542%   $124.2919   $124.29   $124.30   $124.30  
  Purchase #2 $27.58   11.399%   $30.7238   $30.72   $30.70   $30.70  
  Purchase #3 $223.77   12.303%   $251.3004   $251.30   $251.30   $251.30  
  Purchase #4 $241.84   9.873%   $265.7169   $265.72   $265.70   $265.70  
  Purchase #5 $153.32   9.295%   $167.5711   $167.57   $167.55   $167.60  
  Purchase #6 $211.77   6.800%   $226.1704   $226.17   $226.15   $226.20  
  Purchase #7 $154.56   13.761%   $175.829   $175.83   $175.85   $175.80  
  7 purchase totals = $1,129.50       $1,241.6035   $1,241.60   $1,241.55   $1,241.60