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 $89.66   7.196%   $96.1119   $96.11   $96.10   $96.10  
  Purchase #2 $233.45   12.507%   $262.6476   $262.65   $262.65   $262.60  
  Purchase #3 $43.68   11.198%   $48.5713   $48.57   $48.55   $48.60  
  Purchase #4 $35.67   8.650%   $38.7555   $38.76   $38.75   $38.80  
  Purchase #5 $205.74   3.221%   $212.3669   $212.37   $212.35   $212.40  
  Purchase #6 $95.64   3.158%   $98.6603   $98.66   $98.65   $98.70  
  Purchase #7 $203.88   4.393%   $212.8364   $212.84   $212.85   $212.80  
  7 purchase totals = $907.72       $969.9499   $969.96   $969.90   $970.00