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 $89.43   6.544%   $95.2823   $95.28   $95.30   $95.30  
  Purchase #2 $91.52   5.776%   $96.8062   $96.81   $96.80   $96.80  
  Purchase #3 $80.28   13.388%   $91.0279   $91.03   $91.05   $91.00  
  Purchase #4 $228.70   4.844%   $239.7782   $239.78   $239.80   $239.80  
  Purchase #5 $239.68   5.391%   $252.6011   $252.60   $252.60   $252.60  
  Purchase #6 $55.73   6.689%   $59.4578   $59.46   $59.45   $59.50  
  Purchase #7 $235.39   3.397%   $243.3862   $243.39   $243.40   $243.40  
  7 purchase totals = $1,020.73       $1,078.3397   $1,078.35   $1,078.40   $1,078.40