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 $148.70   8.165%   $160.8414   $160.84   $160.85   $160.80  
  Purchase #2 $36.86   4.412%   $38.4863   $38.49   $38.50   $38.50  
  Purchase #3 $170.91   3.815%   $177.4302   $177.43   $177.45   $177.40  
  Purchase #4 $20.52   10.774%   $22.7308   $22.73   $22.75   $22.70  
  Purchase #5 $139.62   5.552%   $147.3717   $147.37   $147.35   $147.40  
  Purchase #6 $37.83   11.490%   $42.1767   $42.18   $42.20   $42.20  
  Purchase #7 $25.68   13.399%   $29.1209   $29.12   $29.10   $29.10  
  7 purchase totals = $580.12       $618.1580   $618.16   $618.20   $618.10