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 $80.86   8.137%   $87.4396   $87.44   $87.45   $87.40  
  Purchase #2 $96.98   9.241%   $105.9419   $105.94   $105.95   $105.90  
  Purchase #3 $200.67   9.265%   $219.2621   $219.26   $219.25   $219.30  
  Purchase #4 $111.54   4.693%   $116.7746   $116.77   $116.75   $116.80  
  Purchase #5 $111.30   11.395%   $123.9826   $123.98   $124.00   $124.00  
  Purchase #6 $209.59   5.350%   $220.8031   $220.80   $220.80   $220.80  
  Purchase #7 $248.91   7.453%   $267.4613   $267.46   $267.45   $267.50  
  7 purchase totals = $1,059.85       $1,141.6652   $1,141.65   $1,141.65   $1,141.70